swish (n.)
1820, sound of something moving through the air, from swish (v.); sense of "effeminate homosexual" is 1930s in homosexual slang, probably from notion of mincing motion. Related: Swishy (adj.).
swish (v.)
1756 (intransitive); 1799 (transitive), probably imitative of the sound made by something brushing against or through something. Related: Swished; swishing.