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I just found out that luster in British English was actually lustre. This was something that I did not know before.
Are there any other words that behave like this? Why? (According to what?)

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Imposing '-er' over '-re' on words from old French is one of the orthographic simplifications by Webster when he wrote his dictionary of American English. These alternate spellings are particular to the USA, and are otherwise not preferred.

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See chapter, December, diameter, etc. – kiamlaluno Feb 13 '11 at 18:24
+1 for the facts, which are relevant and not mentioned in other answers. But the tone seems a bit unnecessarily disparaging! If an American told me that I was “quite incorrect” for writing ‘theatre’ while I’m here, I’d find that pretty rude. But they don’t, usually: they accept us writing ‘theatre’, ‘colour’, etc, and most Brits, Aussies etc. accept Americans writing ‘theater’, ‘color’… – PLL Feb 13 '11 at 19:11
@PLL: 's why it got a -1 from me. This is an international site, not a "British English Only" site. So, "alternate spellings" is wrong in this context. – Jürgen A. Erhard Feb 13 '11 at 21:03
Rereading, I think I came off unintentionally terse in my explanation. Entirely my fault. To rephrase, the '-er' is an American variation, and therefore, unless one is writing in American English, '-re' should be preferred. – smithco Feb 13 '11 at 21:46
@smithco: you can always edit your answer to make it less terse. This will also give downvoters an opportunity to change their mind (otherwise, the downvotes are locked-in). – RegDwigнt Feb 14 '11 at 9:47

According to Wikipedia:

In British usage, some words of French, Latin, or Greek origin end with a consonant followed by -re, with the -re unstressed and pronounced /ər/. Most of these words have the ending -er in the United States. The difference is most common for words ending -bre or -tre: British spellings centre, goitre, kilometre, litre, lustre, mitre, nitre, reconnoitre, saltpetre, spectre, theatre, titre, calibre, fibre, sabre, and sombre all have -er in American spelling.

... Many words spelled with -re in Modern French are spelled with -er in both British and American usage; among these are chapter, December, diameter, perimeter, disaster, enter, filter, letter, member, minister, monster, October, November, number, oyster, parameter, powder, proper, September, sober, and tender.

The ending -cre, as in acre, lucre, massacre, mediocre, is preserved in American English, to indicate the c is pronounced /k/ rather than /s/.

After other consonants, there are not many -re endings ...: louvre and manoeuvre after -v; meagre (but not eager) and ogre after -g; and euchre, ochre, and sepulchre after -ch. In the United States, ogre and euchre are standard; manoeuvre and sepulchre are usually spelled as maneuver and sepulcher; ...

The e preceding the r is retained in American-derived forms of nouns and verbs, for example, fibers, reconnoitered, centering, ... fibres, reconnoitred and centring respectively in British usage. ...

Exceptions. ... include Germanic words like anger, mother, timber, water and Romance words like danger, quarter, river.


More recent French loanwords retain an -re spelling in American English. ... double-entendre, genre, or oeuvre. ... cadre, macabre, maître d', Notre Dame, piastre, and timbre.

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@mplungjan: Link rot happens. – Jon Purdy Feb 13 '11 at 19:47
Full entry added for the lazy and to avoid link rot, which I do not for one second believe is an issue for Wikipedia entries, quite the opposite – mplungjan Feb 14 '11 at 11:26
In my experience with WP, stuff like this will not disappear. Changes are normally more than welcome. We are not talking political borders or pop stars ;) – mplungjan Feb 14 '11 at 13:39
You really should summarize this article and use excerpts from it, rather than copying the entire thing word-for-word. – Kosmonaut Feb 14 '11 at 14:56
see, mp, no good deed goes unpunished! – fortunate1 Feb 14 '11 at 17:18

In English, final unstressed -re after a consonant is pronounced /ər/. Most of the words that are written with final -re in British English are written with final -er in American English to reflect the pronunciation. The list of such words, apart from lustre/luster, includes:

  • calibre/caliber
  • centre/center
  • fibre/fiber
  • goitre/goiter
  • kilometre/kilometer
  • litre/liter
  • mitre/miter
  • nitre/niter
  • reconnoitre/reconnoiter
  • sabre/saber
  • saltpetre/saltpeter
  • spectre/specter
  • theatre/theater
  • titre/titer

There are words that are written with the final -er in both American and British English, even when the original words from which the English words are derived end in re, or contained a consonant cluster like tr:

  • diameter (from Old French diametre)
  • disaster (from Italian disastro)
  • filter (from Old French filtre)
  • monster (from Old French monstre)
  • number (from Old French numbre)
  • oyster (from Old French oistre)
  • perimeter (from Greek perimetros)

Reference: Wapedia.

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"Wapedia" is just a Wikipedia mirror, BTW. – ShreevatsaR Feb 14 '11 at 12:45

There are many words like these: centre, centimetre, fibre, calibre, litre, just to name a few. (Other answers have given good longer lists.) I’m sure there are some exceptions escaping me, but all or almost all of these have the same history:

Generally, the -re forms are older: these words came into English from French, where they were (and mostly, still are) spelled similarly (centre, centimétre), and where the pronunciation reflects the -re ending.

After entering English, the pronunciations became anglicised and no longer matched the spellings — so for proponents of spelling reform, these words were an obvious target. Most influentially, Noah Webster used the -er forms in his dictionary and his ‘Blue-backed Speller’; and (like many of his reforms), they caught on across the US, and are now the standard spellings there.

As far as I know, most other English-speaking countries use the -re forms; but as the influence of American English increases for ESL students, this may well now be changing.

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They don't "behave" like this, they just are different in British (or English) English and American English. And it is, as far as I'm aware, purely historical.

Yes, there are other words with the same "-er"/"-re" difference. "Theater"/"theatre" comes readily to mind.

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American English got rid of many homophones from British English, using one spelling for both meanings. Examples such as kerb/curb, metre/meter, practise/practice, license/licence, etc. All these are used in British English but with different meanings for the different spellings.

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"kerb" is actually a more recent spelling than "curb." Apparently, it comes from French "courber." – sumelic Mar 4 at 22:21

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