I was teaching my young nephew some math the other day, and from discussing the typical sort of word problems he's encountering in class, I noticed that the "-th" suffix adds a distinct meaning to adjectives. For example:

  • If a ship is long, it has length.
  • If a woman is wide, she has width.
  • If a person is strong, he possesses strength.
  • If what I say is true, I'm speaking truth.
  • A lumbering panda moving slow is full of sloth.

Now, I've learned some linguistics from English L&U, and I'm guessing this "-th" suffix is an affix that changes adjectives into nouns. My questions are: What exactly is this "-th" suffix adding to the meaning? Secondly, does the "-th" originate from a separate word in Old English? Lastly, is there something to say about the vowel shifts that seems to be occurring in some of the transformations (e.g., strong going to strength) that somehow fits in with the ablaut system of strong verbs/weak verbs, that I learned of from the excellent responses to my previous question?

  • 2
    I upvoted your question, it's interesting :) And it would be so on the Linguistics.SE too!
    – Alenanno
    May 20, 2011 at 11:28
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    Very interesting question! I am agreeing more and more with the usefulness of the Linguistics site.
    – Kit Z. Fox
    May 20, 2011 at 11:31
  • +1 and for the record, I think -th sounds much better than -ness. -ness is quite overused, especially since there's often already a word available: why accurateness instead of just accuracy? Also consider the similar growgrowth, from OE -ð(u).
    – Jon Purdy
    May 20, 2011 at 18:00
  • 1. en.wiktionary.org/wiki/-th 2. Old English -ðu, , from Proto-Germanic -*itho, abstract noun suffix, from PIE -*ita (cf. Sanskrit -tati-; Greek -tet-; Latin -tati-, as in libertatem "liberty" from liber "free"). etymonline.com/index.php?term=-th 3 See also, books.google.co.in/books?id=aDhGlKL3h00C&pg=PA586
    – Kris
    Jan 13, 2014 at 12:38

5 Answers 5


It is, as you say, a nominalising suffix, that goes back at least to Common Germanic. It usually surfaces as "-th" in English, but as "-t" after a (historical) "-(g)h": "height", "weight", "sight", "flight".

The vowel alternations are mostly a matter of length (though I admit that the "-ong"/"-ength" alternation sounds a bit like IE ablaut). "Wide" in Old and Middle English was bisyllabic, with a long vowel, whereas "widþ" had one closed syllable and therefore a short vowel. Only the long vowel went waltzing round the mouth in the Great Vowel Shift. Thinking about it, this particular alternation may go back to a time when the IE ablaut was operating, but I'm not sure.

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    Note that many do say heighth [haɪ(t)θ] or [haɪʔθ] for height, by analogy with those words that do have th, and since gh is null in modern English. I'd say weighth is less common, and for other -ght words it's hardly heard at all. People can complain all they want about it being incorrect, but hey, the only reason it was -t and not -th in the first place is gone, so why not?
    – Jon Purdy
    May 20, 2011 at 18:08
  • I don't recall ever hearing that pronunciation, but the OED lists [haɪθ] and indeed the spelling 'highth'.
    – Colin Fine
    May 21, 2011 at 0:32
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    @JonPurdy The four of us were dressed in the heighth of fashion, ... A Clockwork Orange ... BTW, I say heighth*/*highth in the singular but heights in the plural :shrug:
    – AnWulf
    Feb 20, 2012 at 2:46
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    I believe strong/strength is umlaut. We also see this in filth, from foul + th.
    – herisson
    Dec 2, 2016 at 14:16

In general, the suffix -th that creates nouns from adjectives comes from Proto-Germanic *-iþō.

Since this was already a suffix in Proto-Germanic, it definitely was not a separate word in Old English. In fact, it seems to descend from a Proto-Indo-European suffix, the same one that is the origin of Latin -(i)tas (which shows up in English borrowed words as -(i)ty).

The vowel shifts are not related to ablaut. There are two main causes:

  • umlaut, or i-affection: although the original i in the suffix was lost by the time of Old English, it left a trace by making a preceding vowel front, changing a to æ or e, o to e, and u to y (which became i later on).
  • regular shortening of long vowels before consonant clusters, and inconsistent shortening of long vowels in some cases before final single consonants


  • the Old English adjective strang/strong "strong" corresponded to the noun strængþ(u)/strengþ(u) "strength," and the Old English adjective lang/long "long" corresponded to the noun lengþ(u) "length". These both show umlaut.

  • In Old English, the noun corresponding to slāw "slow" was slǣwþ, with the expected umlaut, but the word later got remodeled to have the vowel of the adjective: sloth. Sloth has two pronunciations in modern English: it may have a shortened vowel, like cloth (from Old English clāþ) or it may not, like oath (from Old English āþ).

  • The adjective foul is actually related to the noun filth. The latter shows umlaut and shortening: the words descend from Old English fūl and fȳlþ.

  • the noun width shows shortening of the originally long vowel seen in wide.

  • the adjective true corresponds to Old English triewe/treowe. (It would be more etymologically accurate if we used the spelling "trew" in modern English, but we don't because English spelling is a mess). Since the vowel in Old English (ie or eo) was front already, it didn't change in the noun triewþ/treowþ "truth".

  • breadth has an interesting history. It does show umlaut, as can be seen from comparing it to the adjective broad (from Old English brād; the development of the vowel in modern English is irregular). ‎But in Old English, it actually did not have the -th suffix: the umlaut was due to a Proto-Germanic form suffixed with something like -j- or -i-, which was lost resulting in brǣdu (cognate to German Breite). The suffix -th was added to it in Middle English by analogy with words like length and width. The vowel also ended up being shortened, which is not surprising since the word ends in a consonant cluster "dth" and the Middle English vowel that corresponds to the "ea" in this word (/ɛː/) was sometimes shortened even before a single consonant (as in bread, threat, death, deaf).

  • Thank you, that was interesting. Am I right in thinking that troth meaning fidelity and loyalty as in "and thereto I give thee my troth" also derives from the same root as "true"?
    – BoldBen
    Jan 20, 2019 at 13:44
  • @BoldBen: Right; "troth" and "truth" originated as variants of the same word.
    – herisson
    Jan 20, 2019 at 13:45

The purpose of the suffix -th is, yes, to make adjectives into nouns. It can also change verb actions into nouns as well i.e. 'grow' into 'growth'

This suffix actually came from an Old English letter, -þ, which actually also had the same function of turning verbs and adjectives into nouns.

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    Idiot: Not that I'm doubting the truth of this, but it would be nice to see a corroborating reference. Such as merriam-webster.com/word/word.php?date=Apr-26-2010 May 20, 2011 at 12:50
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    Rather, the suffix has had the sound /þ/ or variants thereof since Old English, when it was usually written "þ". A linguistic element or sound cannot come from a letter, which is merely a way of writing down a sound.
    – Colin Fine
    Feb 21, 2012 at 0:52

th as suffix changes the verb or adjective to a noun - no dispute there. What does making it a noun add to the meaning? It often seems to mean a state of: eg Strength - a state of strong. Health as a state of healing, Width as a state of wide, etc.


Th suffix represents a continued on in the word example believeth opposed to just saying believe believeth means continue to believe,saith means continue to say

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    That's an entirely different -th, nothing to do with this question at all. It's also wrong: ‘believeth’ is simply an older form of ‘believes’, there is no difference in meaning. Jan 13, 2014 at 10:13

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