Definition of fortress noun from the Oxford Advanced Learner's Dictionary

 

fortress

 noun
noun
BrE BrE//ˈfɔːtrəs//
 
; NAmE NAmE//ˈfɔːrtrəs//
 
Historic buildings
 
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a building or place that has been made stronger and protected against attack a fortress town enclosed by four miles of ramparts Fear of terrorist attack has turned the conference centre into a fortress. See related entries: Historic buildings Word Origin Middle English: from Old French forteresse ‘strong place’, based on Latin fortis ‘strong’.Extra examples The fortress fell after a nine-day siege. They took refuge in the fortress. The medieval fortress town is enclosed by four miles of ramparts.
See the Oxford Advanced American Dictionary entry: fortress