Source : Webster's Revised Unabridged Dictionary (1913)

Flank \Flank\ (fl[a^][ng]k), v. t. [imp. & p. p. {Flanked}
   (fl[a^][ng]kt); p. pr. & vb. n. {Flanking}.] [Cf. F.
   flanquer. See {Flank}, n., and cf. {Flanker}, v. t.]
   1. To stand at the flank or side of; to border upon.

            Stately colonnades are flanked with trees. --Pitt.

   2. To overlook or command the flank of; to secure or guard
      the flank of; to pass around or turn the flank of; to
      attack, or threaten to attack; the flank of.