The Collaborative International Dictionary of English v.0.48:
Swim \Swim\, n. 1. The act of swimming; a gliding motion, like that of one swimming. --B. Jonson. [1913 Webster] 2. The sound, or air bladder, of a fish. [1913 Webster] 3. A part of a stream much frequented by fish. [Eng.] [1913 Webster] 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.] [1913 Webster]