A fortress in a commanding position in or near a city.(noun)
A stronghold or fortified place; a bulwark.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "citadel" in a sentence
"In the original Persian text, the citadel is rendered as the Arg-i Kabul."
"The citadel is warded against magical intrusion-we can't just 'pop' in and out, even if such a thing were easily possible."
"The very famous and ancient Anglo-Saxon language, whose citadel is supposed to be confined to the charmed circle over which Bow Bells presides, is just about to conquer the continent of Australia, and I am inclined to think that the people who are fighting against it are fighting against fate."