What is the exact rule regarding the plural/singular 'year'?

Which one is correct and why:

  • A five-year degree
  • A five-years degree

As in a degree that takes five years to complete, of course.

Furthermore do you capitalize any word, and is it proper form to use numerals (5-year(s))?


Speaking in simple words, when you form a compound word to function as an adjective by joining a cardinal number with another noun with a hyphen between them, you use the other noun (say year) in the singular. such as a one-year degree, a five-year degree, a one-story building, a three-story building.

  • How could you possibly use a "plural cardinal number" in this case? "Ones-year degree"? "Fives-story building"? Cardinal numbers are very rarely plural at all and certainly not in this construction. – Catija Sep 26 '15 at 6:26
  • Catija, Sorry. I have edited my answer. – Khan Sep 26 '15 at 10:49
  • You still haven't explained why you believe you can use both singular and plural cardinal numbers in this case. – Catija Sep 26 '15 at 14:04

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