Swim, n.
 1. The act of swimming; a gliding motion, like that of one swimming.
 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.]
 swim bladder
      n : an air-filled sac near the spinal column in many fishes that
          helps maintain buoyancy [syn: air bladder]