Etymology
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stonefly (n.)
mid-15c., from stone (n.) + fly (n.). So called because the larval forms abound under stones of steams.
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flown 
past participle of fly (v.), from Middle English flogen, flowen. Also formerly the past participle of flow (v.).
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firefly (n.)

also fire-fly, "An insect which has the faculty of becoming luminous" [Century Dictionary], 1650s, from fire (n.) + fly (n.). Ancient Greek had kysolampis "firefly, beetle with a tail that lights up at night," from kysos, kysthos "buttocks" + lampein "to shine."  

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flyer (n.)
also flier, mid-15c., "that which flies, thing or creature that flies," agent noun of fly (v.1). Meaning "something that goes fast" is from 1795. Meaning "speculative investment, financial venture" is from 1846 (on the notion of a "flying leap"). Meaning "small handbill or fly-sheet" is from 1889, U.S. slang (originally especially of police bulletins), on notion of "made to be scattered broadcast." Meaning "aviator" (1916) developed in World War I. Related: Fliers; flyers.
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dragonfly (n.)

common name of a neuropterous predatory insect of the group Libellulina, with a long, slender body, large eyes, and two pairs of large, membranous wings, 1620s, from dragon + fly (n.). An older name for it was adderbolt (late 15c.), for its shape, also devil's darning-needle.

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fugleman (n.)

also fugelman, "expert soldier placed in front of a regiment or company in exercises as an example to the others," a mangled borrowing of German Flügelmann "leader of a file," literally "wing-man," from Flügel "wing" (related to fliegen "to fly;" see fly (v.1)) + Mann (from PIE root *man- (1) "man").

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*pleu- 
Proto-Indo-European root meaning "to flow."

It forms all or part of: fletcher; fledge; flee; fleet (adj.) "swift;" fleet (n.2) "group of ships under one command;" fleet (v.) "to float, drift; flow, run;" fleeting; flight (n.1) "act of flying;" flight (n.2) "act of fleeing;" flit; float; flood; flotsam; flotilla; flow; flue; flugelhorn; fluster; flutter; fly (v.1) "move through the air with wings;" fly (n.) "winged insect;" fowl; plover; Pluto; plutocracy; pluvial; pneumo-; pneumonia; pneumonic; pulmonary.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit plavate "navigates, swims;" Greek plynein "to wash," plein "to navigate," ploein "to float, swim," plotos "floating, navigable," pyelos "trough, basin;" Latin plovere "to rain," pluvius "rainy;" Armenian luanam "I wash;" Old English flowan "to flow;" Old Church Slavonic plovo "to flow, navigate;" Lithuanian pilu, pilti "to pour out," plauju, plauti "to swim, rinse."
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flee (v.)

Old English fleon, flion "take flight, fly from, avoid, escape" (contracted class II strong verb; past tense fleah, past participle flogen), from Proto-Germanic *fleuhanan "to run away" (source also of Old High German fliohan, Old Norse flöja, Old Frisian flia, Dutch vlieden, German fliehen, Gothic þliuhan "to flee"), probably from PIE *pleuk-, extended form of root *pleu- "to flow," but Boutkan is not convinced. Also compare fly (v.2).

Weak past tense and past participle fled emerged in Middle English under influence of Scandinavian. Old English had a transitive form, geflieman "put to flight, banish, drive away," which came in handy in the Anglo-Saxon Chronicle. Related: fled; Fleeing.

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flying (adj.)

early 15c., replacing forms from Old English fleogende "flying, winged;" present-participle adjective from fly (v.1). The meaning "attached so as to have freedom of movement" (1670s) is the source of the nautical use (flying jib, etc.). Meaning "designed for rapid movement" (especially in military terms, e.g. flying camp) is from 1660s; meaning "passing, hasty, temporary, rapidly constructed" is from 1763.

Flying fish is from 1510s; flying buttress "segment of an arch projecting from a solid mass and serving to stabilize a wall" is from 1660s. Flying Dutchman, ghost ship off the Cape of Good Hope, is attested since 1790 [John MacDonald "Travels in Various Parts of Europe, Asia, and Africa"]. Various accounts are given of how it came to be condemned to sail the sea, beating against head-winds, till the day of judgment. It is said that the ship sometimes hails vessels with the request that they will take letters home.

Flying colors (1706) probably is from the image of a naval vessel with the national flag bravely displayed. Flying machine is from 1736 as a theoretical device. Flying saucer first attested 1947, though the image of saucers for unidentified flying objects is from at least 1880s.

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butterfly (n.)

common name of any lepidopterous insect active in daylight, Old English buttorfleoge, evidently butter (n.) + fly (n.), but the name is of obscure signification. Perhaps based on the old notion that the insects (or, according to Grimm, witches disguised as butterflies) consume butter or milk that is left uncovered. Or, less creatively, simply because the pale yellow color of many species' wings suggests the color of butter. Another theory connects it to the color of the insect's excrement, based on Dutch cognate boterschijte. Also see papillon.

Applied to persons from c. 1600, originally in reference to vain and gaudy attire; by 1806 in reference to transformation from early lowly state; in reference to flitting tendencies by 1873. The swimming stroke so called from 1935. As a type of mechanical nut, 1869. Butterflies "light stomach spasms caused by anxiety" is from 1908. Who breaks a butterfly upon a wheel? is from Pope.

The butterfly effect is a deceptively simple insight extracted from a complex modern field. As a low-profile assistant professor in MIT's department of meteorology in 1961, [Edward] Lorenz created an early computer program to simulate weather. One day he changed one of a dozen numbers representing atmospheric conditions, from .506127 to .506. That tiny alteration utterly transformed his long-term forecast, a point Lorenz amplified in his 1972 paper, "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?" [Peter Dizikes, "The Meaning of the Butterfly," The Boston Globe, June 8, 2008]

A truth known for ages to poets and philosophers (atomists) which modern science ponders as a possible fact.

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