A group of words which have a different meaning when used together from the one they would have if you took the meaning of each word separately.
kill someone or an animal off
to kill all of a group of people or creatures.
Lefty set out to kill Max and his boys off.
Phrasal verbs are compound verbs that result from combining a verb with an adverb or a preposition. The resulting compound verb is idiomatic.
A compilation of 50 phrasal verbs.