Phrasal verbs, also called two-word verbs, are idiomatic expressions wherein the second element of the verb (the adverb or particle) is not necessarily predictable.
Phrasal Verb:
hound someone or an animal down
Meaning:
to pursue and capture someone or an animal.
Example:
I will hound the killer down if it takes me the rest of my life.
A phrase that combines a verb with a preposition or adverb or both and that functions as a verb whose meaning is different from the combined meanings of the individual words.