1. To slosh, splash, or swirl around (inside of something). A: "How can you tell the ball is waterlogged?" B: "I can hear water swishing around in it." Don't drink too much water, or you'll feel it swishing around while you're running.

2. To cause some liquid to slosh, splash, or swirl around (inside of something). In this usage, a noun or pronoun is used between "swish" and "around." Why do you swish your wine around in the glass like that? Swish the liquid around to help the salt dissolve into it.