the fleshy or muscular part of the side of an animal, between the ribs and the hip. see illust. of beef.-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.-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.-the side of any building.-that part of the acting surface of a gear wheel tooth that lies within the pitch line.-to stand at the flank or side of; to border upon.-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.-to border; to touch.-to be posted on the side.