stronghold
strong (adj.) + hold (n.)
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/icons/point.icon What is the difference between stronghold and fortress ? | HiNative
"Fortress" refers specifically to a physical fortification like a castle, while "stronghold" means about the same thing but is often used metaphorically.
noun
1. a place that has been fortified so as to protect it against attack.
｟古｠ 要塞, 砦(fort); (防衛上･軍事上の)拠点.
2. a place where a particular cause or belief is strongly defended or upheld:
(活動などの)本拠地, 中心点, 牙城; (動物種の)一大生息地
e.g. a Republican stronghold.