bridgehead

noun

1. 1

   An area around the end of a bridge.

2. 2

   A fortification around the end of a bridge.

3. 3

   An area of ground on the enemy's side of a river or other obstacle, especially one that needs to be taken and defended in order to secure an advance.

4. 4

   Either of the two atoms in different parts of a molecule that are connected by a bridge of two or more other atoms