the most important word in a phrase, which explains the truth of a situation.
He wants more time for his private life, private being the operative word. Photographers are not allowed anywhere near his family.
the operative word
The word in a statement that is most important in understanding its intended or true meaning. The police released a statement saying they have not yet filed any charges. The operative word being "yet."
the ˌoperative ˈword
used to emphasize that a particular word or phrase is the most important one in a sentence: I was in love with her — ‘was’ being the operative word.