waistlineEnglishMerriam-Webster Dictionary/span>ˈsi-tə-dᵊl , -ˌdel \ a fortress that commands a citystronghold Definition 1 : a fortress that commands (see command entry 1 sense 2c) a city2 : stronghold //… the nation's citadel of health research … — Constance Holden //a citadel of higher education