Source : Webster's Revised Unabridged Dictionary (1913)

Bridgehead \Bridge"head`\, n.
   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
   t[^e]te-de-pont.

Source : WordNet®

bridgehead
     n 1: 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" [syn: {foothold}]
     2: a defensive post at the end of a bridge nearest to the enemy