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Old English fleoge "fly, winged insect," from Proto-Germanic *fleugjon (cf. Old Saxon fleiga, Old Norse fluga, Middle Dutch vlieghe, Dutch vlieg, Old High German flioga, German Fliege "fly); literally "the flying (insect)" (cf. Old English 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 Old English plural in -n (cf. oxen) gradually normalized 13c.-15c. to -s. Fly on the wall "unseen observer" first recorded 1881. An Old English word for "curtain" was fleonet "fly-net." Fly-swatter first attested 1917. Fly-fishing is from 1650s.
"to soar through air," Old English fleogan "to fly" (class II strong verb; past tense fleag, past participle flogen), from West Germanic *fleuganan (cf. Old Saxon and Old High German fliogan, Old Norse flügja, Old Frisian fliaga, Middle Dutch vlieghen, Dutch vliegen, German fliegen), from PIE *pleu- "flowing, floating" (see pluvial).
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." The noun sense of "a flight, flying" is from mid-15c. Baseball fly ball attested by 1866. Slang phrase fly off the handle "lose one's cool" dates from 1825. To do something on the fly is 1856, apparently from baseball.
"run away," Old English fleon (see flee). Fleogan and fleon were often confused in Old English, too. Modern English distinguishes in preterite: flew/fled.
slang, "clever, alert, wide awake," late 18c., perhaps from fly (n.) on the notion of the insect being hard to catch. Other theories, however, trace it to fledge or flash. Slang use in 1990s might be a revival or a reinvention.
Any of numerous two-winged insects of the order Diptera.
Any of numerous insects of the order Diptera, having one pair of wings and large compound eyes. Flies include the houseflies, horseflies, and mosquitoes. See more at dipteran.
[the first adjective sense, ''clever, alert, etc,'' is of unknown origin, though it is conjectured that it may refer to the difficulty of catching a fly in midair, that it may be cognate with fledge and hence mean ''accomplished, proven, seasoned,'' and that it is a corruption of fla, a shortening of flash; the third verb sense, ''succeed, persuade, etc,'' is fr a cluster of jokes and phrases having to do with the Wright Brothers' and others' efforts to get something off the ground and make it fly; the two adjective senses involve either a survival or a revival of an early 19thcentury British underworld term of unknown origin]
Heb. zebub, (Eccl. 10:1; Isa. 7:18). This fly was so grievous a pest that the Phoenicians invoked against it the aid of their god Baal-zebub (q.v.). The prophet Isaiah (7:18) alludes to some poisonous fly which was believed to be found on the confines of Egypt, and which would be called by the Lord. Poisonous flies exist in many parts of Africa, for instance, the different kinds of tsetse. Heb. 'arob, the name given to the insects sent as a plague on the land of Egypt (Ex. 8:21-31; Ps. 78:45; 105:31). The LXX. render this by a word which means the "dog-fly," the cynomuia. The Jewish commentators regarded the Hebrew word here as connected with the word _'arab_, which means "mingled;" and they accordingly supposed the plague to consist of a mixed multitude of animals, beasts, reptiles, and insects. But there is no doubt that "the _'arab_" denotes a single definite species. Some interpreters regard it as the Blatta orientalis, the cockroach, a species of beetle. These insects "inflict very painful bites with their jaws; gnaw and destroy clothes, household furniture, leather, and articles of every kind, and either consume or render unavailable all eatables."