Bridgehead

Definitions

1. An area around the end of a bridge.
2. A fortification around the end of a bridge.
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. Either of the two atoms in different parts of a molecule that are connected by a bridge of two or more other atoms
   physical

Equivalents

Examples

“He believed the invasion would happen⟳ elsewhere and it wasn't until late in the afternoon and long after the Allied forces had established a bridgehead that Hitler was convinced of the need⟳ to do something.”

CEFR level