Words with prefixes or suffixes that need to be emphasized: ex-husband, re-emphasize, President-elect.
Proper nouns with prefixes attached:ex-Catholic, neo-Nazi.
Groups of words which serve an adjectival or adverbial function:twentieth-century philosophy, never-ending story.
Note the difference between a high school (noun) and a high-school (adjective) teacher.
Two-word numbers (between 21 and 99) and two-word fractions:forty-one, thirty-fifth, four-fifths. A larger number is written thus: three hundred and sixty-five.
