According to Wiktionary, the British spelling of "vaporize" is vaporise, not vapourise as one might expect from the word vapour (and similarly, the Canadian spelling is still vaporize, not vapourize). The words "laborious" and "coloration" suffer from the same problem, and yet "favourable" doesn't. Why is this so?

And in case you think Wiktionary is a disputable source, the Cambridge Dictionary has no entry for vapourise either.

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    And the British spelling of "laborious" is "laborious". The British spelling of "honorarium" is "honorarium". Not to mention the British spelling of "coloration", which is (usually) "coloration". Did you expect English spelling to make sense? – Peter Shor Feb 22 '14 at 5:02
  • I'm actually trying to ask about the general case of those words, so I'll include them as examples in the question itself. – Joe Z. Feb 22 '14 at 5:17
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    Words ending in -our lose the spurious u when turned into longer derived forms. – tchrist Feb 22 '14 at 7:06
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    @Kris: It's about the u. I've edited the question to make that clearer. – Joe Z. Feb 22 '14 at 19:06
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    In French, it's vapeur and vaporiser. Two different vowels. I suspect this is the cause of the difference in spelling. Ditto for French labeur and laborieux. – Peter Shor Feb 22 '14 at 19:21

"Vapourise" or "vapourize" does seem to be considered an incorrect spelling of this word in any form of English. To understand why, you need to know a little bit about the history of words spelled with ⟨our⟩.

⟨or⟩ normally occurs in the spelling of Latin, as opposed to French, roots

Many Latinate words came into English from French (by which I mean, not modern French, but the Anglo-Norman dialect that was spoken by French speakers living in Great Britain). The British English practice of using the spelling ⟨our⟩ in some words where Americans use ⟨or⟩ usually reflects the phonetic development of Latin "or" to French "our" (in Modern French, as Peter Shor mentions in a comment, the "ou" has often changed further to "eu"). Therefore, in words that are taken directly from Latin (or at least, treated as if they were taken directly from Latin), without the intermediary of French, we would generally expect to see ⟨or⟩ instead of ⟨our⟩.

⟨or⟩ is used before suffixes that strongly prefer to come after Latin roots (-⁠ation, -⁠ious)

Certain suffixes, such as -(a)-(t)-ion, strongly "prefer" to come after Latin roots. So for example, corresponding to the verb destroy (which shows some French sound changes) we have the noun destruction (which preserves the Latin spelling of the root). Another example is deceive, deception. The spelling difference between colour, coloration parallels the audible difference for some other sets of words; hopefully this is helpful for remembering it.

The Latin spelling ⟨or⟩ is also used in general before the suffix -ious, which explains labour vs. laborious.

⟨our⟩ is used before inflectional suffixes (-⁠ed, -⁠ing) and suffixes that strongly prefer to come after whole words (-⁠hood, -⁠ship, -⁠ment)

Other suffixes, such as all English inflectional suffixes, can come after complete English words of any origin (and they can't come after Latin roots unless the root can be used as an independent word). Inflectional suffixes for verbs include -ed, -(e)s, -ing; so we write the inflected forms of destroy as destroyed, destroyed, destroying. In this case, destructed does exist, but it's the past tense of a different verb, to destruct. And we can only say deceived, deceives, deceiving: there isn't any such word as *decepted (which would be the past tense of a hypothetical verb to *decept). Likewise, ⟨colored⟩ would only make sense as the past tense of a verb to ⟨color⟩, which does not exist in the type of British English you're talking about.

Native English derivational suffixes such as -hood, -ship and -ful also fall into this category. So there is no change between neighbour and neighbourhood, saviour and saviourhood (or saviourship), or colour and colourful. In addition, the derivational suffix -ment, which comes from French, generally comes after a stand-alone verb, not a bare Latin root (so Collins gives discolourment, from to discolour, and marks discolorment as an American spelling).

Fowler (1926; repub. 2009) also mentions -ist and -ite as suffixes in this category. Labourist, behaviourist, colourist all prefer ⟨our⟩ in British English. However, florist does use Latin ⟨or⟩, as does arborist, from Latin arbor. Interestingly, humorist seems to be more common than humourist in British English (although both exist); see the Google Ngram Viewer and the British National Corpus (which has "humorist" with a frequency of 15, vs. "humourist" with a frequency of 4). I don't think -ite is really common enough to be worth worrying about, but the example Fowler gives is "Labourite".

Of course, words that are standardly spelled with word-final ⟨or⟩ in British English will keep this spelling when suffixed: motorist < motor, terrorist < terror.

Either ⟨or⟩ or ⟨our⟩ seems possible in theory before the suffix -able, but the standard spelling is currently ⟨ourable⟩

Some other suffixes, such as -able, behave both ways, and can come after either a whole word of any origin, or a Latinate root. This suffix did exist in Latin, and it can be used in English after Latin roots (although for some words the spelling may change to -ible) as in destructible. However, -able is also highly productive after regular English verbs of any origin, so we also can say destroyable (even if some people might consider it less elegant). In some cases, we don't even use the word formed from the Latin root, only the one formed from an English verb (we say deceivable, not deceptible). I think this explains why both favourable and favorable are possible in principle (to find out which is actually used more, it's necessary to consult a dictionary or corpus of British English).

Fowler advises ⟨our⟩ before -able, and this is backed up by a look at the Google Ngram Viewer for "colorable" vs. "colourable" in the British English corpus.

⟨or⟩ is usual before the suffix -ise/-ize, which prefers to come after Latin roots (although it can also come after English words)

The suffix -ize/-ise is Latinate, and often prefers to come after a Latin root (we say anglicize, not *englishize) but in modern English there are also many words formed by attaching -ize to whole English words (the Oxford English Dictionary lists foreignize, jeopardize, womanize among others). I think this is what leads to variation in the spelling of words such as colorise/colourise and vaporise/vapourise. There's actually similar variation with the words crystallize/crystalize and metallize/metalize (where the Latin stems, seen in crystalline and metallic, had double ll, but the independent English nouns crystal and metal have single l).

Dictionaries rarely list vapourise/vapourize: it is not usual and is likely to be considered incorrect

Tristan r left the following useful comment referencing several British dictionaries that have entries for "vaporise":

the Cambridge English Dictionary says (UK usually vaporise). See dictionary.cambridge.org/dictionary/british/vaporize?q=vaporize The Longman English Dictionary says the same ldoceonline.com/dictionary/vaporize

I did not find any dictionaries indexed by OneLook Dictionary Search that have an entry for "vapourise", aside from Wiktionary, which calls it a "Misspelling of vaporise."

Based on this, I would guess that many British English writers would indeed consider it a misspelling.

The following question is also quite relevant: Should "glamourous" be considered incorrect?


British English spelling is — or has been — more variable than one might imagine. (Microsoft Word’s spelling dictionary and its ilk seem currently to be forcing a standardization — or ‘standardisation’, as it would have me write.) Using individually compiled printed dictionaries as reference, here are some relevant extracts from Chambers and the Oxford English Dictionary (OED).

Chambers (contemporary iPhone version and printed 1993 ed.)

‘vaporize’ or ‘vaporise’


‘favourable’ or ‘favorable’ (esp US)

OED (encyclopedic edition 1991)



‘favourable’ (US ‘favorable’)

OED (1926)

‘vaporize’ (18thC citations also include ‘vaporise-’), but also ‘vapourized’, citing usage by Macaulay as equivalent to ‘vapoured’, having the different meaning, ‘filled with vapour’.


‘favourable’, ‘favorable’

This edition (unlike the later) gives both spellings, ‘favour’ and ‘favor’, with the note: “As with other words of the same ending, the spelling with -our is preferred in the British Isles, while in the US -or is more common.” In its examples the latest use of the spelling ‘favorable’ is by Hobbes in 1651 (although there is one example of ‘favorably’ from 1872).

(N.B. ‘-ise’ seems only to have become more frequent than ‘-ize’ in British English usage in the latter half of the twentieth century. The OED (1928), for example, includes ‘recognize’ but not ‘recognise’; and this is still the case for a pocket edition I have from the ’50s.)

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    The Oxford Dictionary to this day still lists -ize as the preferred form, so that might have just been to save space on the pocket edition. – Joe Z. Jul 2 '16 at 1:08
  • I have done a some quick checking and as my amendment indicates it is not a question of using the pocket edition of the OED. Also, I found that my large mid-century English–French (Collins) and English–Italian dictionaries only have ‘recognize’. However using the index of a copy of the Oxford Dictionary of Quotations I do find examples of ‘recognise’ and ‘organise’ from 19th-century writers, in addition to the ‘-ize’ spelling. The 15th and 16th century original usages quoted by the OED are spelt ‘-ise’, with the first ‘-ize’ spellings apparently in the 17th century. – David Jul 2 '16 at 8:25

My dictionary, Gyldendal's Red Dictionary translates from Danish to British English and vice versa and is the most reliable one in Denmark (which is very reliable, even though Denmark is a small country).

It knows the word "favourable" and not the word "favorable". And it spells "vaporize" as so, just like the American spelling. Cambridge on the other hand has results for both "favourable" and "favorable", but neither one has "vaporise", Cambridge even redirects to "vaporize" when searching for it.

Also my British spell checking plug-in for Firefox agrees on "favourable", "vaporize" and is even cool with "vaporise", but it puts a red line under "favorable". This plug-in might not be that reliable, though, I don't even know who made it.

  • Hello. Welcome to English Language and Usage. Your fourth and fifth paragraphs have nothing to do with answering the question. Please do not write sentences that don't answer the question in the answer box. – user140086 Jul 1 '16 at 16:44
  • Thanks. I would have written it in a comment if I was allowed to, but new users aren't, which is understandable. I think at least my forth paragraph was pretty well connected with the first three, and even though it didn't answer the question it was a conclusion to the first three that did. But yes, we must obey the rules. – MÅNEMANN3 Jul 4 '16 at 10:20

In British English, when words have an '-our' suffix (eg favour, humour & vapour), get another suffix (eg '-able', '-ous' & '-ise' ), they lose the 'u' (eg favorable, humorous & vaporise). This is a standard rule, therefore there isn't the word 'favourable' in British or American English.

There is a similar rule with the suffix '-ous': Curious ----> Curiosity But in this case, pronunciation changes as well. This applies for both British and American English.

  • Not quite: see oxforddictionaries.com/definition/english/favourable – Merk May 25 '14 at 2:03
  • Nor Chambers. See my post. – David Jul 1 '16 at 21:11
  • You should define what you mean by "another suffix." Existing comments and answers have shown that this is not always true for the suffixes -able and -ise; it's definitely not true for inflectional suffixes such as -ed, which the original poster seems to be confused about (he mentioned in a comment "I thought ["Words ending in -our lose the spurious u when turned into longer derived forms"] was the rule as well, but apparently words like "coloured" or "favourable" don't have this rule applied to them"). – herisson Jul 2 '16 at 4:55

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