Some noun compounds take a hyphen !

Hello there,
Could anybody tell me if there is ever a rule to use a hyphen?
I have noticed " take-off" and “takeover” !! One is hyphened while the other is not !
Please explain

Know that the present trend is to avoid hyphenation when there is no ambiguity. As a rule, the hyphen is used in compound nouns/adjectives (comrade-in arms, good-for-nothing etc), for figures written in words (twenty-one, ninety-nine etc) and in splitting syllables for setting the page (govern-ment, beauti-ful etc). You will also find many other words which used to be hyphenated in the past are now let free (either written together or sans hyphens) as in ‘hangover’, ‘five year old’, ‘get together’ etc etc.