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Should I say "3 half days" or "3 half-days" or "3 half-day"? I mean I want to refer to, for example, the a.m. of Monday, the p.m. of Wednesday, and the a.m. of Friday, together.

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Related english.stackexchange.com/questions/1366/… – user19148 Oct 8 '12 at 21:12
How about 36 hours? Anyway, 'three half days' is accurate (says what it means and means what it says) but probably won't mean much to people until you say 'three of either a morning, for example...' – Mitch Oct 8 '12 at 21:28
"36 hours" is not "three half-days". It's equal in terms of the quantity of time, but not the literal meaning. – qazwsx Oct 8 '12 at 21:31
Isn't the quantity of time really the literal meaning? If not, you need to give an explanation of the meaning that you want to help us decide. Examples aren't enough. For example, in giving exams, an exam period is either the morning, the afternoon, or the evening (three equal allowable periods). You might understand that, but giving an example of them is not enough. – Mitch Oct 8 '12 at 21:39
OP gave a specific example: "the a.m. of Monday, the p.m. of Wednesday, and the a.m. of Friday". I'm assuming those are business hours or classroom hours so it's like saying, "...half of Monday, half of Wednesday and half of Friday" - in other words, 3 half days. – Kristina Lopez Oct 9 '12 at 3:10
up vote 4 down vote accepted

You should say:

three half-days

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Why "three half days" is wrong? – qazwsx Oct 8 '12 at 21:32
Because you must use a hyphen in something like “a half-day” or “a quarter-hour”. Otherwise you need to make it longer: half a day, a quarter of an hour. – tchrist Oct 8 '12 at 21:37
Why both "half a day" and "a half of a day" sound right but "quarter an hour" doesn't? – qazwsx Oct 9 '12 at 1:28
@user1664196 Because you can use “half a something” but not “quarter a something”: half a dozen, half a bushel, half a pound, half a foot, half an hour, half a crown. However, you can run a quarter the distance. – tchrist Oct 9 '12 at 1:44
@KristinaLopez No, those are still nouns, just used attributively. The OED provides the example of “their half-wit uncle” [from the Times], and says that that’s an “attrib.” noun. The adjective would be half-witted, as in “A half-witted king, every day growing feebler in mind.” [Bancroft]. Noun–noun compounds have always been around in English, but there use has increased in modern times. This is a real headache for people doing natural language processing and computational linguistics on a computer. – tchrist Oct 9 '12 at 3:45

I think the answer should be "three half-day". For Ex: I have taken three half-day leaves.

We cant't use plural nouns with compound adjectives.

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"Leave" isn't a countable noun, so this doesn't work. You could say "Three half-day periods of leave" but that's rather convoluted. The question seems sto be asking for a preference between "three half days of leave", "three half-days of leave" and "three half-day of leave". – David Richerby Aug 24 '15 at 8:04

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