- fly (n.)
- O.E. fleoge, from P.Gmc. *fleugjon (cf. O.S. fleiga, O.N. fluga, M.Du. vlieghe, Ger. Fliege "fly); lit. "the flying (insect)" (cf. O.E. fleogende "flying"), from same source as fly(v.1). Originally "any winged insect" (hence butterfly, etc.); long used by farmers and gardeners for any insect parasite. The O.E. plural in -n (cf. oxen) gradually normalized 13c.-15c. to -s. Slang adj. meaning "clever, alert, wide awake" first recorded 18c., perhaps from the notion of the insect being hard to catch (other theories, however, trace it to fledge or flash); 1990s use may be a revival or a reinvention. Fly on the wall "unseen observer" first recorded 1949. An O.E. word for "curtain" was fleonet "fly-net." Fly-swatter first attested 1917. Fly-fishing is from 1650s.
- fly (v.1)
- "to soar through air," O.E. fleogan (class II strong verb; past tense fleag, pp. flogen), from W.Gmc. *fleuganan (cf. O.H.G. fliogan, O.N. flügja, M.Du. vlieghen, Ger. fliegen), from PIE *pleu- "flowing, floating" (cf. Lith. plaukiu "to swim"). Notion of "flapping as a wing does" led to noun sense of "tent flap" (1810), which yielded (1844) "covering for buttons that close up a garment." Slang phrase fly off the handle "lose one's cool" dates from 1825. On the fly is 1851.
- fly (v.2)
- "run away," O.E. fleon (see flee). Fleogan and fleon were often confused in O.E., too. Mod.Eng. distinguishes in preterite: flew/fled.