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.]