(n.) The chief tower, also called the keep; a massive tower in ancient castles, forming the strongest part of the fortifications.
Thesaurus Entries
bastion, beachhead, blockhouse, bridgehead, bunker, castle, citadel, donjon, fasthold, fastness, fort, fortress, garrison, garrison house, hold, keep, martello, martello tower, mote, motte, peel, peel tower, pillbox, post, rath, safehold, strong point, stronghold, tower, tower of strength, ward
