Whim

google

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late 17th century: of unknown origin. whim (sense 2) (mid 18th century) is a transferred use.

wiktionary

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Clipping of whim-wham.

Compare whimbrel.

etymonline

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whim (n.)

1640s, "play on words, pun," shortened from whimwham "fanciful object" (q.v.). Meaning "caprice, fancy, sudden turn or inclination of the mind" first recorded 1690s, probably a shortened form of whimsy.