"act of flying," Old English flyht "a flying, act or power of flying," from Proto-Germanic *flukhtiz (source also of Dutch vlucht "flight of birds," Old Norse flugr, Old High German flug, German Flug "flight"), from Proto-Germanic *flugti-, suffixed form of PIE root *pleu- "to flow."
Spelling altered late 14c. from Middle English fliht (see fight (v.)). Sense of "swift motion" is from mid-13c.. Meaning "an instance of flight" is 1785, originally of ballooning. Sense of "a number of things passing through the air together" is from mid-13c. Meaning "series of stairs between landings" is from 1703. Figuratively, "an excursion" of fancy, imagination, etc., from 1660s. Flight-path is from 1908; flight-test (v.) from 1919; flight-simulator from 1947 (originally in rocketry); flight-attendant from 1946.
"act of fleeing," c. 1200, flihht, not found in Old English, but presumed to have existed and cognate with Old Saxon fluht, Old Frisian flecht "act of fleeing," Dutch vlucht, Old High German fluht, German Flucht, Old Norse flotti, Gothic þlauhs, from Proto-Germanic *flugti-, suffixed form of PIE root *pleu- "to flow." To put (someone or something) to flight "rout, defeat" is from late 14c., the earlier verb form do o' flight (early 13c.).