A hyphen is used to connect compound adjectives when they come after a noun.

Hyphens are not needed for compound numbers like 'twenty-one' or 'thirty-two.'

A hyphen should be used in 'hot water bottle' to clarify that it is a bottle for hot water.

The phrase 'a two-year-old child' requires hyphens, but 'The child is two years old' does not.

'Ex-wife' and 'mid-October' do not require hyphens.

Hyphens are always necessary between words when writing compound nouns.

The hyphen is used to split words between syllables at the end of a line in writing.

Words like 'de-ice' and 're-sign' are correctly hyphenated to avoid confusion with other words.