Definitions of castellum - OneLook Ava Bailey • Apr 07, 2026 general Definitions from Wiktionary (castellum)▸ noun: (historical) A small Roman detached fort or fortlet used as a watch tower or signal station.castrum, castellany, castlet, casern, castle, bastion, fort, blockhouse, fabrica, wall tower, more...▸ Words similar to castellum▸ Usage examples for castellum▸ Idioms related to castellum▸ Civic discussion about castellum (New!)▸ Popular adjectives describing castellum▸ Words that often appear near castellum▸ Rhymes of castellum▸ Invented words related to castellum