"act of flying," Old English flyht "a flying, flight," from Proto-Germanic *flukhtiz (cf. Dutch vlucht "flight of birds," Old Norse flugr, Old High German flug, German Flug "flight"), from root of *fleugan "to fly" (see fly (v.1)).
Spelling altered late 14c. from Middle English fliht (see fight (v.)). Meaning "an instance of flight" is 1785, originally of ballooning. Meaning "series of stairs between landings" is from 1703.