1.  bridgehead(n = noun.location) foothold - an area in hostile territory that has been captured and is held awaiting further troops and supplies; "an attempt to secure a bridgehead behind enemy lines"; "the only foothold left for British troops in Europe was Gibraltar"
is a kind of combat area, combat zone
has particulars: airhead, beachhead

2.  bridgehead(n = noun.location) - a defensive post at the end of a bridge nearest to the enemy;
is a kind of post, station

   A fortification commanding the extremity of a bridge nearest the enemy, to insure the preservation and usefulness of the bridge, and prevent the enemy from crossing; a tête-de-pont. [1913 Webster]

bridgehead, n. Mil. a fortified position held on the enemy's side of a river or other obstacle.