Flimsy

google

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early 18th century: probably from flimflam.

wiktionary

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Origin uncertain. First used in the 18th century. Perhaps a metathesis of film +‎ -s +‎ -y; or related to flimflam.

etymonline

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flimsy (adj.)

1702, of unknown origin, perhaps a metathesis of film (n.) "gauzy covering" + -y (2). Figuratively (of arguments, etc.) from 1750s. Related: Flimsily; flimsiness.