Swim \Swim\, n. 1. The act of swimming; a gliding motion, like that of one swimming. --B. Jonson. 2. The sound, or air bladder, of a fish. 3. A part of a stream much frequented by fish. [Eng.] {Swim bladder}, an air bladder of a fish. {To be in the swim}, to be in a favored position; to be associated with others in active affairs. [Colloq.]