Which one is the correct (or more commonly used) form: "3-month retreat" or "3-months retreat"? How about "3-day" vs. "3-days" and "3-week" vs. "3-weeks" in the same context? (This is retreat as in meditation retreat and for U.S. English.)

marked as duplicate by FumbleFingers, Hellion, aedia λ, phenry, user66974 Aug 9 '14 at 13:27

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In American English, you'd use the singular. So "3 day weekend" or "8 week course" or, yes, "3 month retreat".

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    +1 And no hyphen either? – Drux Aug 7 '14 at 11:23
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    @Drux there's no particularly consistent rule there, IIRC. The hyphen is not incorrect, nor is it's omission. – LessPop_MoreFizz Aug 7 '14 at 11:25
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    There is a consistent rule for hyphens, it's just people who are not consistent about using it. Search for related questions. – Neeku Aug 7 '14 at 11:32
  • @Neeku Thx. I'm usually applying rules from The Elements of Style which (if memory serves) would recommend one (but not two) hyphens. (Any rule better be consistent :) – Drux Aug 7 '14 at 11:36
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    Yes @Drux. If each adjective alone doesn't make sense being used with the noun, then you must use a hyphen. Neither "8 course" nor "week course" make sense, so "8-week course" is correct. Obviously no hyphen is needed between the adjective and the noun. – Neeku Aug 7 '14 at 11:39

Perhaps surprisingly, the accepted answer at "A place nearby" but not "A place good" answers this. However, that question title is not an intuitive match for this problem, and the relevant sentence is a bit buried.

In the phrase 3-month retreat, the main noun is retreat and three-month serves as an adjective (or an attributive noun, I suppose). Because it has more than one word, a hyphen is necessary to keep all the parts of that adjective together. Because it's an adjective, it remains month and not months: preceding adjectives are not inflected for number.

This serves for other similar collocations:

  • a six-foot coffin
  • a ten-year-old boy
  • a fifty-six-page book
  • +1 for digging this up and for citing an explicit rule. – Drux Aug 7 '14 at 13:02

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