from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A gate in a fortification designed for sorties.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A small door in a fort or a castle to enable a sally; a postern.
- n. An entryway controlled by two doors or gates, of which each must be closed before the other can open.
from the GNU version of the Collaborative International Dictionary of English
- n. A large port on each quarter of a fireship, for the escape of the men into boats when the train is fired; a large port in an old-fashioned three-decker or a large modern ironclad.
from The Century Dictionary and Cyclopedia
- n. In fortification, a gate or a passage to afford free egress to troops in making a sally.
- n. A large port on each quarter of a fire-ship, for the escape of the crew into boats when the train is fired.
Sorry, no etymologies found.
Positioned on the far left flank of the Allied front in the west, it might — if it could be held — become a sally port from which the Allies could thrust into the flank of the German army in France.