Source : Webster's Revised Unabridged Dictionary (1913)

Flanker \Flank"er\, n.
   One who, or that which, flanks, as a skirmisher or a body of
   troops sent out upon the flanks of an army toguard a line of
   march, or a fort projecting so as to command the side of an
   assailing body.

         They threw out flankers, and endeavored to dislodge
         their assailants.                        --W. Irwing.

Flanker \Flank"er\, v. t. [imp. & p. p. {Flankered}; p. pr. &
   vb. n. {Flankering}.] [See {Flank}, v. t.]
   1. To defend by lateral fortifications. [Obs.] --Sir T.
      Herbert.

   2. To attack sideways. [Obs.] --Evelyn.

Source : WordNet®

flanker
     n 1: a back stationed wide of the scrimmage line; used as a pass
          receiver [syn: {flanker back}]
     2: a soldier who is a member of a detachment assigned to guard
        the flanks of a military formation