a sudden change; especially : a sudden change in someone's mood or behavior.
Source: Merriam-Webster's Learner's Dictionary. Examples:
On a whim, he sold everything and left the city for the beautiful wilderness of
Alaska, but his act of
Borrowing from French
Comedy ... than he could ever imagine. But then a pesky girl materializes to make
his life a living hell. His perfect girlfriend now thinks that he is involved with this
a. An impulsive change of mind: "I find it a relief that plagues and cancers ... are the result of the impartial—and comprehensible—forces of evolution rather than ...