An idiom is defined as - a group of words in a fixed order that has a particular meaning that is different from the meanings of each word on its own.
butter (someone) up or butter up (someone)
to flatter someone
The man is trying to butter up his boss so that he can leave early on Friday.
List of common idioms, their meanings and examples of their usage in sentences
The language peculiar to a people or to a district, community, or class