When does a word get hyphenated?

Answer 1

In typography, the hyphen was widely used for words too long for a single line of type, to con-

tinue them on the next line with a break between syllables. However, right justification is now accomplished with proportional text.

- In grammar, words used together to have a specialized meaning would be joined by hyphens, such as the term "ten-year-old" so that the reader would be forewarned reading the text that the ten was not being followed by a plural noun. Other nouns also signal a connection, such as mother-in-law.

- Similarly, compound modifiers (paired nouns and adjectives) are joined to avoid confusion, as in the compound adjectives work-related, second-rate, custom-built, and split-level. Some prefixes primarily used hyphens, as in pre-galvanized and re-piercing. However compound nouns are increasingly being run together as in cooperate, reelect and preeminent.

- The text forms of paired numbers from twenty-one through ninety-nine are hyphenated as adjectives.