Source : Webster's Revised Unabridged Dictionary (1913)

Flail \Flail\, n. [L. flagellum whip, scourge, in LL., a
   threshing flail: cf. OF. flael, flaiel, F. fl['e]au. See
   {Flagellum}.]
   1. An instrument for threshing or beating grain from the ear
      by hand, consisting of a wooden staff or handle, at the
      end of which a stouter and shorter pole or club, called a
      swipe, is so hung as to swing freely.

            His shadowy flail hath threshed the corn. --Milton.

   2. An ancient military weapon, like the common flail, often
      having the striking part armed with rows of spikes, or
      loaded. --Fairholt.

            No citizen thought himself safe unless he carried
            under his coat a small flail, loaded with lead, to
            brain the Popish assassins.           --Macaulay.

Source : WordNet®

flail
     n : an implement consisting of handle with a free swinging stick
         at the end; used in manual threshing
     v 1: give a thrashing to; beat hard [syn: {thrash}, {thresh}, {lam}]
     2: move like a flail; thresh about; "Her arms were flailing"
        [syn: {thresh}]