Whim/wɪm/ Definition 1 of 3Pro Tip 1/3Spontaneous Action Refers to an action taken without planning or forethought, often on impulse. She quit her job on a whim, surprising everyone. Pro Tip 2/3Emotionally Driven Indicates an action or decision guided more by emotions than logic. On a whim, he booked a flight to see his best friend. Pro Tip 3/3Unpredictable Behavior Suggests a person's behavior cannot be predicted because of sudden desires. She redecorated her room on a whim.