From Longman Dictionary of Contemporary English cit‧a‧del /ˈsɪtədəl, -del/ noun 1 a strong fort (=small castle) built in the past as a place where people could go for safety if their city was attacked SYN fortress 2 → the citadel of something Examples from the Corpus citadel The term is a diminutive of "city", meaning "little city", because it is a smaller part of the. It may be a castle, fortress, or fortified center. A citadel is the core fortified area of a town or city. In this seventeenth-century plan of the fortified city of Casale Monferrato the citadel is the large star-shaped structure on the left. What does citadel mean? Information and translations of citadel in the most comprehensive dictionary definitions resource on the web. Definition of citadel in the dictionary.