Fleeting

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Old English flēotan ‘float, swim’, of Germanic origin; related to Dutch vlieten and German fliessen, also to flit and float.

wiktionary

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From Middle English fleten(“to float”), from Old English flēotan(“to float”), from Proto-Germanic *fleutaną, from Proto-Indo-European *plewd-.

etymonline

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fleeting (adj.)

early 13c., "fickle, shifting, unstable," from Old English fleotende "floating, drifting," later "flying, moving swiftly," from present participle of fleotan "to float, drift, flow" (see fleet (v.)). Meaning "existing only briefly" is from 1560s. Related: Fleetingly.