The Collaborative International Dictionary of English v.0.48:

Fly \Fly\, n.; pl. Flies (fl[imac]z). [OE. flie, flege, AS.
   fl[=y]ge, fle['o]ge, fr. fle['o]gan to fly; akin to D. vlieg,
   OHG. flioga, G. fliege, Icel. & Sw. fluga, Dan. flue. [root]
   84. See Fly, v. i.]
   1. (Zool.)
      (a) Any winged insect; esp., one with transparent wings;
          as, the Spanish fly; firefly; gall fly; dragon fly.
      (b) Any dipterous insect; as, the house fly; flesh fly;
          black fly. See Diptera, and Illust. in Append.
          [1913 Webster]

   2. A hook dressed in imitation of a fly, -- used for fishing.
      "The fur-wrought fly." --Gay.
      [1913 Webster]

   3. A familiar spirit; a witch's attendant. [Obs.]
      [1913 Webster]

            A trifling fly, none of your great familiars. --B.
                                                  Jonson.
      [1913 Webster]

   4. A parasite. [Obs.] --Massinger.
      [1913 Webster]

   5. A kind of light carriage for rapid transit, plying for
      hire and usually drawn by one horse. [Eng.]
      [1913 Webster]

   6. The length of an extended flag from its staff; sometimes,
      the length from the "union" to the extreme end.
      [1913 Webster]

   7. The part of a vane pointing the direction from which the
      wind blows.
      [1913 Webster]

   8. (Naut.) That part of a compass on which the points are
      marked; the compass card. --Totten.
      [1913 Webster]

   9. (Mech.)
      (a) Two or more vanes set on a revolving axis, to act as a
          fanner, or to equalize or impede the motion of
          machinery by the resistance of the air, as in the
          striking part of a clock.
      (b) A heavy wheel, or cross arms with weights at the ends
          on a revolving axis, to regulate or equalize the
          motion of machinery by means of its inertia, where the
          power communicated, or the resistance to be overcome,
          is variable, as in the steam engine or the coining
          press. See Fly wheel (below).
          [1913 Webster]

   10. (Knitting Machine) The piece hinged to the needle, which
       holds the engaged loop in position while the needle is
       penetrating another loop; a latch. --Knight.
       [1913 Webster]

   11. The pair of arms revolving around the bobbin, in a
       spinning wheel or spinning frame, to twist the yarn.
       [1913 Webster]

   12. (Weaving) A shuttle driven through the shed by a blow or
       jerk. --Knight.
       [1913 Webster]

   13.
       (a) Formerly, the person who took the printed sheets from
           the press.
       (b) A vibrating frame with fingers, attached to a power
           to a power printing press for doing the same work.
           [1913 Webster]

   14. The outer canvas of a tent with double top, usually drawn
       over the ridgepole, but so extended as to touch the roof
       of the tent at no other place.
       [1913 Webster]

   15. One of the upper screens of a stage in a theater.
       [1913 Webster]

   16. The fore flap of a bootee; also, a lap on trousers,
       overcoats, etc., to conceal a row of buttons.
       [1913 Webster]

   17. (Baseball) A batted ball that flies to a considerable
       distance, usually high in the air; also, the flight of a
       ball so struck; as, it was caught on the fly. Also called
       fly ball. "a fly deep into right field"
       [1913 Webster +PJC]

   18. (Cotton Manuf.) Waste cotton.
       [Webster 1913 Suppl.]

   Black fly, Cheese fly, Dragon fly, etc. See under
      Black, Cheese, etc. -- Fly agaric (Bot.), a mushroom
      (Agaricus muscarius), having a narcotic juice which, in
      sufficient quantities, is poisonous. -- Fly block
      (Naut.), a pulley whose position shifts to suit the
      working of the tackle with which it is connected; -- used
      in the hoisting tackle of yards. -- Fly board (Printing
      Press), the board on which printed sheets are deposited by
      the fly. -- Fly book, a case in the form of a book for
      anglers' flies. --Kingsley.Fly cap, a cap with wings,
      formerly worn by women. -- Fly drill, a drill having a
      reciprocating motion controlled by a fly wheel, the
      driving power being applied by the hand through a cord
      winding in reverse directions upon the spindle as it
      rotates backward and forward. --Knight.Fly fishing, the
      act or art of angling with a bait of natural or artificial
      flies; fishing using a fly[2] as bait. --Walton. -- --
   Fly fisherman, one who fishes using natural or artificial
      flies[2] as bait, especially one who fishes exclusively in
      that manner. -- Fly flap, an implement for killing
      flies. -- Fly governor, a governor for regulating the
      speed of an engine, etc., by the resistance of vanes
      revolving in the air. -- Fly honeysuckle (Bot.), a plant
      of the honeysuckle genus (Lonicera), having a bushy stem
      and the flowers in pairs, as L. ciliata and L.
      Xylosteum. -- Fly hook, a fishhook supplied with an
      artificial fly. -- Fly leaf, an unprinted leaf at the
      beginning or end of a book, circular, programme, etc. --
   Fly maggot, a maggot bred from the egg of a fly. --Ray.

   Fly net, a screen to exclude insects.

   Fly nut (Mach.), a nut with wings; a thumb nut; a finger
      nut.

   Fly orchis (Bot.), a plant (Ophrys muscifera), whose
      flowers resemble flies.

   Fly paper, poisoned or sticky paper for killing flies that
      feed upon or are entangled by it.

   Fly powder, an arsenical powder used to poison flies.

   Fly press, a screw press for punching, embossing, etc.,
      operated by hand and having a heavy fly.

   Fly rail, a bracket which turns out to support the hinged
      leaf of a table.

   Fly rod, a light fishing rod used in angling with a fly.

   Fly sheet, a small loose advertising sheet; a handbill.

   Fly snapper (Zool.), an American bird (Phainopepla
      nitens), allied to the chatterers and shrikes. The male
      is glossy blue-black; the female brownish gray.

   Fly wheel (Mach.), a heavy wheel attached to machinery to
      equalize the movement (opposing any sudden acceleration by
      its inertia and any retardation by its momentum), and to
      accumulate or give out energy for a variable or
      intermitting resistance. See Fly, n., 9.

   On the fly (Baseball), still in the air; -- said of a
      batted ball caught before touching the ground..
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

black fly \black fly\, blackfly \blackfly\, (Zool.)
   1. In the United States, a small, venomous, two-winged fly of
      the genus Simulium of several species, exceedingly
      abundant and troublesome in the northern forests; --
      called also buffalo gnat. The larv[ae] are aquatic. It
      sucks the blood of birds as well as humans and other
      mammals.
      [WordNet 1.5 + WordNet 1.5]

   2. A black plant louse, as the bean aphis (Aphis fab[ae]),
      which infests e. g. beans and sugar beets; -- called also
      bean aphid.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

black fly
    n 1: small blackish stout-bodied biting fly having aquatic
         larvae; sucks the blood of birds as well as humans and
         other mammals [syn: blackfly, black fly, buffalo
         gnat]