Source : Webster's Revised Unabridged Dictionary (1913)

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.