Splat

google

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mid 19th century: from obsolete splat ‘split up’; related to split.

wiktionary

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From earlier splat(“to spread flat”), from Middle English splatten, splaten(“to stretch out, extend", also "to split”). Compare dialectal English splat(“flat”).

Onomatopoeia

etymonline

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splat (v.)

"to land with a smacking sound," 1897, probably of imitative origin. As a noun from 1958.