An idiom is defined as - a group of words whose meaning is different from the meanings of the individual words.
Idiom:
play the devil's advocate
Meaning:
to argue against something even if you may agree with it
Example:
I was playing the devil's advocate when I asked my friend about his plan to change jobs.
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.