Why is "letter" not plural in "two letter words"?

For me it's very strange as the equivalent in French would be plural but my English friend finds it totally normal.

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    In French, you would say "mots de deux lettres" right? The equivalent English structure is "words of two letters," where the plural is indeed used. But "two-letter words" (I think it is best to write it with a hyphen) uses a construction which has no exact equivalent in French (just as the French "soupe à l'oignon" construction has no exact equivalent in English).
    – sumelic
    Commented Mar 28, 2017 at 16:51
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    How that is written in French is irrelevant. I bet in German one would write that as a single word, but that doesn't mean you have to concatenate words in English. Commented Mar 29, 2017 at 11:28
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    @DmitryGrigoryev In my understanding the point is not about how it's written in French, rather it's the fact that - unlike words of two letters, which does have an exact French equivalent and both use the plural - the expression two-letter words has no exact equivalent in French, and such English expression needs the singular; same as two-year old. Regardless, I also have the feeling that the hyphen is kind of key here. Commented Mar 29, 2017 at 11:44
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    In french you would use a similar adjective form : un mot doublement lettré if you really want something equivalent, which is not plural either. I agree nobody use such constructs in french.
    – JB.
    Commented Mar 30, 2017 at 8:11
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    @SantiBailors: yes, the hyphen is key. But that should be two-year-old. A two-year-old child is two years old. (Many high-ranking journalists don't get this.)
    – TonyK
    Commented Mar 30, 2017 at 17:20

6 Answers 6


Measure phrases are special noun phrases that we use to explain how long or big or heavy or expensive something is:

  • The programme was ten minutes.
  • The walk was five miles.
  • The meal was twenty pounds.
  • The word is only three letters

These measure phrases all include a number, like one or seven and a noun afterwards. In the examples above these measure phrases are Complements of the verb. You will notice that the nouns are all in the plural, as we expect.

We can also use measure phrases like these to modify nouns:

  • a ten minute programme.
  • a five mile walk.
  • a twenty pound note.
  • a three letter word.

Here, these measure phrases are modifying the nouns programme, walk and note. They are in the same position that we find adjectives in. When we use measure phrases in this way, the noun in the measure phrase is not plural. We see no S on the ends of the words in the measure phrases.

Really this is not very surprising. Why? Well, when we use a noun to modify another noun, we don't usually use plurals (there are exceptions of course). So we usually say:

  • a book collector
  • an anteater
  • a cherry tart

We don't say:

  • *a books collector
  • *an ants eater
  • *a cherries tart
  • 1
    @BillJ I've never really considered 'compound adjectives' based on measure phrases as compound adjectives. I was very surprised today to find that H&P do. I've always regarded them as nominals in attributive function. I don't think there's much (if any) difference between a three mile walk and a twenty dollar bill and a three letter word ... Maybe there is - but I can't see it. Is there any difference in their syntactic properties? Commented Mar 28, 2017 at 16:08
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    I think "three-letter" is a noun-centred compound noun (det+noun) as attributive modifier of "word" in your example. I know dictionaries are unreliable, but they all give "four-letter" as a single noun in "four-letter word". The fact that it is hyphenated is an indication that "four-letter" is single lexeme, not a syntactic construction of modifier + noun (see CGEL p1644)
    – BillJ
    Commented Mar 28, 2017 at 16:55
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    @BillJ We can coordinate the numerals there: "Two, three and four letter words". However, I can see two-letter as a compound noun - but not as a compound adjective, which is what I think H&P would say it was. I'm with you on that. Commented Mar 28, 2017 at 19:08
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    Hi folks, just FYI this answer has been automatically flagged for having a bunch of comments. Can we make sure that the salient points here have been incorporated into the answer and possibly move this into a chat room? I'm reluctant to trim the conversation just yet because I think it's valuable, but I would like to whittle it down eventually.
    – ColleenV
    Commented Mar 29, 2017 at 20:26
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    I've submitted an edit hyphenating the second group, because I was taught that when a multi-word phrase is used as an adjective to modify a noun following it, the phrase is hyphenated, like "ten-minute programme" Commented Mar 29, 2017 at 22:15

You might mean 'two-letter words'.
Be aware that there's a real hyphen between 'two' and 'letter', with which we don't use plural from of the latter word because such a hyphened phrase is used as an adjective, not a noun. For example:

  • I went on a trip of four days after my three-day work was done.
  • A boy of five years and another six-year-old girl.
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    From my observation US writers usually omit the hyphen
    – im_chc
    Commented Mar 28, 2017 at 16:18
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    @im_chc : I see that as well, but I'm afraid it's from ignorance, not because of a grammatical standard. I dislike that practice very much. I also very rarely see the correct use of the hyphen in numbers, such as "one thousand four hundred thirty-eight"
    – MPW
    Commented Mar 28, 2017 at 19:38
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    "A boy of five years old and....?" Really? I would expect "A boy of five years and...."
    – Adam
    Commented Mar 28, 2017 at 20:06
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    @iBug I went ahead and incorporated Adam's suggestion into your answer. The example was ungrammatical with old. However, it is your answer, so please feel free to edit it as you see fit (including rolling back the change if you disagree).
    – user230
    Commented Mar 29, 2017 at 1:37
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    @MrLister The boy is five years old, but he is of five years.
    – DCShannon
    Commented Mar 29, 2017 at 19:51

The measure phrases, such as "two-letter", act as adjectives. We do not pluralize adjectives in English.

Any accurate translation is an equivalent: any phrase that gets across the same meaning, or as close to that meaning as possible. We should never primarily try for a word-for-word translation as our primary goal.

I don't have the "reputation" to comment on others' posts, but let's improve on sentences such as "The meal was 20 pounds." No, the meal cost 20 pounds. (More precise, easily translated, and enjoyable to read.)

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    Also removes ambiguity. "The meal was 20 pounds" could be talking about how much it weighed (that's a heavy meal!)
    – Adeptus
    Commented Mar 29, 2017 at 1:51
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    @Adeptus ... or about eating 20 £; good point. Commented Mar 29, 2017 at 11:49
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    @Adeptus Someone eat a meal weighing 20 lb? I think abbreviations are better here as "lb" and "£" provide no ambiguity but "pound" does.
    – iBug
    Commented Mar 29, 2017 at 14:14

For a combination of 2 reasons:

  1. English has a Germanic grammar, and in Germanic languages, "twoletterword" is one word – a noun! It does not matter that English writes it in 3 words (and as a result, calls it a noun phrase, not a noun) – Germanic languages are older than writing. As far as I know, all other Germanic languages would write it as "twoletterword", which may better represent how they work.
  2. Inflecting a word's constituents is undefined in English. You can only inflect the word as a whole, which is indistinguishable from inflecting the last constituent word (because Germanic compound words read like domain names – most significant part last, which is also where the inflection is).

A compound noun combines multiple nouns to make a new noun, and treats the first noun as an adjective to describe the second noun. Two letters and word are combining to make a new noun. A car salesman is another example. The true noun here is salesman. The word car is there to tell us what kind of salesman they are, so it's being used like an adjective and therefore should not be pluralized like you might a noun. Many compound nouns have no spaces between their constituent nouns, such as keyboard, dishwasher and bathroom. Those examples demonstrate the sheer power of compound nouns--the ability to just take a singular noun and tack it on to another to make a new word. Awesome. And imagine how funny it would sound if you had to add s/es to the first of the two nouns (keysboard, disheswasher, bathsroom...).


The issue is an understanding of the implicit but unspoken content: a 'letter' means an "instance of the letter object' a 'word' means a collection of letter objects

Thus a "two letter word" means two instances of the letter object combined in a word while a word of 20 letters is a collection of size 20 containing letter objects

The English language recognises that the two usages describe different things and therefore have different structures

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