Swish

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mid 18th century: imitative.

etymonline

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swish (v.)

1756 (intransitive); 1799 (transitive), probably imitative of the sound made by something brushing against or through something. Related: Swished; swishing.

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.).