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.
take one's leave of (someone)
to say goodbye to someone and leave (a formal old-fashioned expression)
The Princess took her leave of the Queen and left the room.
List of common idioms, their meanings and examples of their usage in sentences
An idiom is a widely used saying or expression containing a figurative meaning that differs from the phrase's literal meaning.