Flanks of a frontier

Flank Flank (fl[a^][ng]k), n. [F. flanc, prob. fr. L. flaccus flabby, with n inserted. Cf. {Flaccid}, {Flanch}, {Flange}.] 1. The fleshy or muscular part of the side of an animal, between the ribs and the hip. See Illust. of {Beef}. [1913 Webster]

2. (Mil.) (a) The side of an army, or of any division of an army, as of a brigade, regiment, or battalion; the extreme right or left; as, to attack an enemy in flank is to attack him on the side. [1913 Webster]

When to right and left the front

Divided, and to either flank retired. --Milton. (b) (Fort.) That part of a bastion which reaches from the curtain to the face, and defends the curtain, the flank and face of the opposite bastion; any part of a work defending another by a fire along the outside of its parapet. See Illust. of {Bastion}. [1913 Webster]

3. (Arch.) The side of any building. --Brands. [1913 Webster]

4. That part of the acting surface of a gear wheel tooth that lies within the pitch line. [1913 Webster]

{Flank attack} (Mil.), an attack upon the side of an army or body of troops, distinguished from one upon its front or rear.

{Flank company} (Mil.), a certain number of troops drawn up on the right or left of a battalion; usually grenadiers, light infantry, or riflemen.

{Flank defense} (Fort.), protection of a work against undue exposure to an enemy's direct fire, by means of the fire from other works, sweeping the ground in its front.

{Flank en potence} (Mil.), any part of the right or left wing formed at a projecting angle with the line.

{Flank files}, the first men on the right, and the last on the left, of a company, battalion, etc.

{Flank march}, a march made parallel or obliquely to an enemy's position, in order to turn it or to attack him on the flank.

{Flank movement}, a change of march by an army, or portion of one, in order to turn one or both wings of the enemy, or to take up a new position.

{Flanks of a frontier}, salient points in a national boundary, strengthened to protect the frontier against hostile incursion.

{Flank patrol}, detachments acting independently of the column of an army, but patrolling along its flanks, to secure it against surprise and to observe the movements of the enemy. [1913 Webster]