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.
Idiom:
have an in with (someone)
Meaning:
to have a way to request a special favor from someone
Example:
The woman has an in with her boss and can easily get time off.
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.