The Collaborative International Dictionary of English v.0.48:

Flying \Fly"ing\, a. [From Fly, v. i.]
   Moving in the air with, or as with, wings; moving lightly or
   rapidly; intended for rapid movement.
   [1913 Webster]

   Flying army (Mil.) a body of cavalry and infantry, kept in
      motion, to cover its own garrisons and to keep the enemy
      in continual alarm. --Farrow.

   Flying artillery (Mil.), artillery trained to rapid
      evolutions, -- the men being either mounted or trained to
      spring upon the guns and caissons when they change
      position.

   Flying bridge, Flying camp. See under Bridge, and
      Camp.

   Flying buttress (Arch.), a contrivance for taking up the
      thrust of a roof or vault which can not be supported by
      ordinary buttresses. It consists of a straight bar of
      masonry, usually sloping, carried on an arch, and a solid
      pier or buttress sufficient to receive the thrust. The
      word is generally applied only to the straight bar with
      supporting arch.

   Flying colors, flags unfurled and waving in the air; hence:

   To come off with flying colors, to be victorious; to
      succeed thoroughly in an undertaking.

   Flying doe (Zool.), a young female kangaroo.

   Flying dragon.
   (a) (Zool.) See Dragon, 6.
   (b) A meteor. See under Dragon.

   Flying Dutchman.
   (a) A fabled Dutch mariner condemned for his crimes to sail
       the seas till the day of judgment.
   (b) A spectral ship.

   Flying fish. (Zool.) See Flying fish, in the Vocabulary.


   Flying fox (Zool.), see Flying fox in the vocabulary.

   Flying frog (Zool.), either of two East Indian tree frogs
      of the genus Rhacophorus (Rhacophorus nigrapalmatus
      and Rhacophorus pardalis), having very large and broadly
      webbed feet, which serve as parachutes, and enable it to
      make very long leaps.

   Flying gurnard (Zool.), a species of gurnard of the genus
      Cephalacanthus or Dactylopterus, with very large
      pectoral fins, said to be able to fly like the flying
      fish, but not for so great a distance.

   Note: Three species are known; that of the Atlantic is
         Cephalacanthus volitans.

   Flying jib (Naut.), a sail extended outside of the standing
      jib, on the flying-jib boom.

   Flying-jib boom (Naut.), an extension of the jib boom.

   Flying kites (Naut.), light sails carried only in fine
      weather.

   Flying lemur. (Zool.) See Colugo.

   Flying level (Civil Engin.), a reconnoissance level over
      the course of a projected road, canal, etc.

   Flying lizard. (Zool.) See Dragon, n. 6.

   Flying machine, any apparatus for navigating through the
      air, especially a heavier-than-air machine. -- Flying
   mouse (Zool.), the opossum mouse (Acrobates pygm[ae]us), a
      marsupial of Australia. Called also feathertail glider.

   Note: It has lateral folds of skin, like the flying
         squirrels, and a featherlike tail. -- Flying party
      (Mil.), a body of soldiers detailed to hover about an
      enemy. -- Flying phalanger (Zool.), one of several
      species of small marsuupials of the genera Petaurus and
      Belideus, of Australia and New Guinea, having lateral
      folds like those of the flying squirrels. The sugar
      squirrel (Belideus sciureus), and the ariel (Belideus
      ariel), are the best known; -- called also squirrel
      petaurus and flying squirrel. See Sugar squirrel. --
   Flying pinion, the fly of a clock. -- Flying sap (Mil.),
      the rapid construction of trenches (when the enemy's fire
      of case shot precludes the method of simple trenching), by
      means of gabions placed in juxtaposition and filled with
      earth. -- Flying shot, a shot fired at a moving object,
      as a bird on the wing. -- Flying spider. (Zool.) See
      Ballooning spider. -- Flying squid (Zool.), an oceanic
      squid (Ommastrephes Bartramii syn. Sthenoteuthis
      Bartramii), abundant in the Gulf Stream, which is able to
      leap out of the water with such force that it often falls
      on the deck of a vessel. -- Flying squirrel (Zool.) See
      Flying squirrel, in the Vocabulary. -- Flying start, a
      start in a sailing race in which the signal is given while
      the vessels are under way. -- Flying torch (Mil.), a
      torch attached to a long staff and used for signaling at
      night.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flying squirrel \Fly"ing squir"rel\ (? or ?). (Zool.)
   One of a group of squirrels, of the genus Glaucomys
   (formerly Pteromus and Sciuropterus [1913 Webster]),
   especially Glaucomys volans and Glaucomys sabrinus,
   having parachute-like folds of skin extending from the fore
   to the hind legs, which enable them to make very long,
   gliding leaps.
   [1913 Webster +PJC]

   Note: The species of Pteromys are large, with bushy tails,
         and inhabit southern Asia and the East Indies; those of
         Sciuropterus are smaller, with flat tails, and inhabit
         the northern parts of Europe, Asia, and America. The
         American species (Sciuropterus volucella) is also
         called Assapan. The Australian flying squirrels, or
         flying phalangers, are marsupials. See Flying
         phalanger (above).
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Squirrel \Squir"rel\ (skw[~e]r"r[e^]l or skw[i^]r"-; 277), n.
   [OE. squirel, OF. esquirel, escurel, F. ['e]cureuil, LL.
   squirelus, squirolus, scuriolus, dim. of L. sciurus, Gr.
   si`oyros; skia` shade + o'yra` tail. Cf. Shine, v. i.]
   1. (Zool.) Any one of numerous species of small rodents
      belonging to the genus Sciurus and several allied genera
      of the family Sciuridae. Squirrels generally have a
      bushy tail, large erect ears, and strong hind legs. They
      are commonly arboreal in their habits, but many species
      live in burrows.
      [1913 Webster]

   Note: Among the common North American squirrels are the gray
         squirrel (Sciurus Carolinensis) and its black
         variety; the fox, or cat, squirrel (Sciurus cinereus,
         or Sciurus niger) which is a large species, and
         variable in color, the southern variety being
         frequently black, while the northern and western
         varieties are usually gray or rusty brown; the red
         squirrel (see Chickaree); the striped, or chipping,
         squirrel (see Chipmunk); and the California gray
         squirrel (Sciurus fossor). Several other species
         inhabit Mexico and Central America. The common European
         species (Sciurus vulgaris) has a long tuft of hair on
         each ear. The so-called Australian squirrels are
         marsupials. See Petaurist, and Phalanger.
         [1913 Webster]

   2. One of the small rollers of a carding machine which work
      with the large cylinder.
      [1913 Webster]

   Barking squirrel (Zool.), the prairie dog.

   Federation squirrel (Zool.), the striped gopher. See
      Gopher, 2.

   Flying squirrel (Zool.). See Flying squirrel, in the
      Vocabulary.

   Java squirrel. (Zool.). See Jelerang.

   Squirrel corn (Bot.), a North American herb (Dicentra
      Canadensis) bearing little yellow tubers.

   Squirrel cup (Bot.), the blossom of the Hepatica triloba,
      a low perennial herb with cup-shaped flowers varying from
      purplish blue to pink or even white. It is one of the
      earliest flowers of spring.

   Squirrel fish. (Zool.)
      (a) A sea bass (Serranus fascicularis) of the Southern
          United States.
      (b) The sailor's choice (Diplodus rhomboides).
      (c) The redmouth, or grunt.
      (d) A market fish of Bermuda (Holocentrum Ascensione).


   Squirrel grass (Bot.), a pestiferous grass (Hordeum
      murinum) related to barley. In California the stiffly
      awned spikelets work into the wool of sheep, and into the
      throat, flesh, and eyes of animals, sometimes even
      producing death.

   Squirrel hake (Zool.), a common American hake (Phycis
      tenuis); -- called also white hake.

   Squirrel hawk (Zool.), any rough-legged hawk; especially,
      the California species Archibuteo ferrugineus.

   Squirrel monkey. (Zool.)
      (a) Any one of several species of small, soft-haired South
          American monkeys of the genus Callithrix. They are
          noted for their graceful form and agility. See
          Teetee.
      (b) A marmoset.

   Squirrel petaurus (Zool.), a flying phalanger of Australia.
      See Phalanger, Petaurist, and Flying phalanger under
      Flying.

   Squirrel shrew (Zool.), any one of several species of East
      Indian and Asiatic insectivores of the genus Tupaia.
      They are allied to the shrews, but have a bushy tail, like
      that of a squirrel.

   Squirrel-tail grass (Bot.), a grass (Hordeum jubatum)
      found in salt marshes and along the Great Lakes, having a
      dense spike beset with long awns.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flying squirrel
    n 1: nocturnal phalangers that move with gliding leaps using
         parachute-like folds of skin along the sides of the body
         [syn: flying phalanger, flying opossum, flying
         squirrel]