noun (n)

• an area in hostile territory that has been captured and is held awaiting further troops and supplies(noun.location)

  Example:
  An attempt to secure a bridgehead behind enemy lines.
  

  Synonym:
  foothold
  

  source: wordnet30
• a defensive post at the end of a bridge nearest to the enemy(noun.location)

  source: wordnet30
• 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.(noun)

  source: webster1913