An idiom is a group of words, or in other words, a phrase that has a meaning different from the literal meaning of the words in it.
Idiom:
lord it over (someone)
Meaning:
to act as the superior and master of someone, to be bossy over someone
Example:
The supervisor likes to lord it over the other members of the staff.
List of common idioms, their meanings and examples of their usage in sentences
An expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements or in its grammatically atypical use of words.