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.
strike something down [for a court]
to invalidate a ruling or law.
The higher court struck the ruling of the lower court down.
A phrase that consists of a verb with a preposition or adverb or both, the meaning of which is different from the meaning of its separate parts.
A compilation of 50 phrasal verbs.