on the fly

on the fly

verb (used without object), flew or for 11, 19, flied, flown, fly·ing.

  1. to move through the air using wings.
  2. to be carried through the air by the wind or any other force or agency: bits of paper flying about.
  3. to float or flutter in the air: flags flying in the breeze.
  4. to travel in an aircraft or spacecraft.
  5. to move suddenly and quickly; start unexpectedly: He flew from the room.
  6. to change rapidly and unexpectedly from one state or position to another: The door flew open.
  7. to flee; escape.
  8. to travel in space: The probe will fly past the planet.
  9. to move or pass swiftly: How time flies!
  10. to move with an aggressive surge: A mother fox will fly at anyone approaching her kits.
  11. Baseball.
    1. to bat a fly ball: He flied into right field.
    2. to fly out.
  12. Informal. to be acceptable, believable, or feasible: It seemed like a good idea, but it just wouldn’t fly.

verb (used with object), flew or for 11, 19, flied, flown, fly·ing.

  1. to make (something) float or move through the air: to fly a kite.
  2. to operate (an aircraft, spacecraft, or the like).
  3. to hoist aloft, as for display, signaling, etc.: to fly a flag.
  4. to operate an aircraft or spacecraft over: to fly the Pacific.
  5. to transport or convey by air: We fly merchandise to Boston.
  6. to escape from; flee: to fly someone’s wrath.
  7. Theater.
    1. to hang (scenery) above a stage by means of rigging supported by the gridiron.
    2. to raise (scenery) from the stage or acting area into the flies.

noun, plural flies.

  1. a strip of material sewn along one edge of a garment opening for concealing buttons, zippers, or other fasteners.
  2. a flap forming the door of a tent.
  3. Also called tent fly. a piece of canvas extending over the ridgepole of a tent and forming an outer roof.
  4. an act of flying; a flight.
  5. the course of a flying object, as a ball.
  6. Baseball. fly ball.
  7. British. a light, covered, public carriage drawn by one horse; hansom; hackney coach.
  8. Machinery. a horizontal arm, weighted at each end, that pivots about the screw of a press so that when the screw is lowered the momentum of the fly will increase the force of the press.
  9. Also called fan. Horology. a regulating device for chime and striking mechanisms, consisting of an arrangement of vanes on a revolving axis.
  10. Printing.
    1. (in some presses) the apparatus for removing the printed sheets to the delivery table.
    2. Also called flyboy.(formerly) a printer’s devil employed to remove printed sheets from a press.
  11. (on a flag)
    1. the horizontal dimension of a flag as flown from a vertical staff.
    2. the end of the flag farther from the staff.Compare hoist(def 7).
  12. flies. Also called fly loft. Theater. the space above the stage used chiefly for storing scenery and equipment.
  13. Nautical. a propellerlike device streamed to rotate and transfer information on speed to a mechanical log.

Verb Phrases

  1. fly out, Baseball, Softball. to be put out by hitting a fly ball that is caught by a player of the opposing team.


  1. fly blind,
    1. to operate an airplane, especially during conditions of poor visibility, relying solely on instruments for guidance.
    2. to proceed with a complex task in the absence of directions by using one’s own ability to determine what procedures to follow.
  2. fly in the face of, to act in defiance of (authority, custom, etc.).Also fly in the teeth of.
  3. fly off the handle. handle(def 16).
  4. go fly a kite, Slang.
    1. to put up with or get used to matters as they stand.
    2. to confine oneself to one’s own affairs.
    3. to cease being a nuisance: If she gets mad enough she’ll tell me to go fly a kite.
  5. let fly,
    1. to hurl or propel (a weapon, missile, etc.).
    2. to give free rein to an emotion: She let fly with a barrage of angry words.
  6. on the fly,
    1. during flight; before falling to the ground: to catch a baseball on the fly.
    2. hurriedly; without pausing: We had dinner on the fly.

verb flies, flying, flew or flown

  1. (intr) (of birds, aircraft, etc) to move through the air in a controlled manner using aerodynamic forces
  2. to travel over (an area of land or sea) in an aircraft
  3. to operate (an aircraft or spacecraft)
  4. to float, flutter, or be displayed in the air or cause to float, etc, in this wayto fly a kite; they flew the flag
  5. to transport or be transported by or through the air by aircraft, wind, etc
  6. (intr) to move or be moved very quickly, forcibly, or suddenlyshe came flying towards me; the door flew open
  7. (intr) to pass swiftlytime flies
  8. to escape from (an enemy, place, etc); fleehe flew the country
  9. (intr; may be foll by at or upon) to attack a person
  10. (intr) to have a sudden outbursthe flew into a rage again
  11. (intr) (of money, etc) to vanish rapidly
  12. (tr) falconry (of hawks) to fly at (quarry) in attackperegrines fly rooks
  13. (tr) theatre to suspend (scenery) above the stage so that it may be lowered into view
  14. fly a kite
    1. to procure money by an accommodation bill
    2. to release information or take a step in order to test public opinion
  15. fly high informal
    1. to have a high aim
    2. to prosper or flourish
  16. fly in the face of See face (def. 19)
  17. fly off the handle informal to lose one’s temper
  18. fly the coop US and Canadian informal to leave suddenly
  19. go fly a kite US and Canadian informal go away
  20. let fly informal
    1. to lose one’s temper (with a person)she really let fly at him
    2. to shoot or throw (an object)

noun plural flies

  1. Also called: fly front (often plural) a closure that conceals a zip, buttons, or other fastening, by having one side overlapping, as on trousers
  2. Also called: fly sheet
    1. a flap forming the entrance to a tent
    2. a piece of canvas drawn over the ridgepole of a tent to form an outer roof
  3. a small air brake used to control the chiming of large clocks
  4. the horizontal weighted arm of a fly press
    1. the outer edge of a flag
    2. the distance from the outer edge of a flag to the staffCompare hoist (def. 9)
  5. British a light one-horse covered carriage formerly let out on hire
  6. Australian and NZ an attemptI’ll give it a fly
  7. printing
    1. a device for transferring printed sheets from the press to a flat pile
    2. Also called: flyhanda person who collects and stacks printed matter from a printing press
    3. a piece of paper folded once to make four pages, with printing only on the first page
  8. (plural) theatre the space above the stage out of view of the audience, used for storing scenery, etc
  9. rare the act of flying

noun plural flies

  1. any dipterous insect, esp the housefly, characterized by active flightSee also horsefly, blowfly, tsetse fly, crane fly
  2. any of various similar but unrelated insects, such as the caddis fly, firefly, dragonfly, and chalcid fly
  3. angling a lure made from a fish-hook dressed with feathers, tinsel, etc, to resemble any of various flies or nymphs: used in fly-fishingSee also dry fly, wet fly
  4. (in southern Africa) an area that is infested with the tsetse fly
  5. drink with the flies Australian slang to drink alone
  6. fly in amber See amber (def. 2)
  7. fly in the ointment informal a slight flaw that detracts from value, completeness, or enjoyment
  8. fly on the wall a person who watches others, while not being noticed himself or herself
  9. there are no flies on him informal he is no fool

adjective flyer or flyest slang

  1. mainly British knowing and sharp; smart
  2. mainly Scot furtive or sneaky


  1. on the fly mainly Scot in secret; sneakily

adj.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. n.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. v.1“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. v.2“run away,” Old English fleon (see flee). Fleogan and fleon were often confused in Old English, too. Modern English distinguishes in preterite: flew/fled. n.

  1. Any of numerous two-winged insects of the order Diptera.

  1. 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.

In a hurry, on the run, as in I picked up some groceries on the fly. The transfer of this expression, which literally means “in midair or in flight,” dates from the mid-1800s.

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