1. A fortress or a strongly fortified building in or near a city, used as a place of protection or refuge: It is obvious that more citadels are needed by many cities and countries in our modern times to protect their citizens against attacks by terrorists who have no regard for the lives of innocent people!
2. An organization or institution which strongly defends a particular way of life or principle; center of strength: Tom's university was a citadel which prepared students to face their futures with skills that will make it possible for them to live better lives.
3. Etymology: from 1586, "fortress commanding a city", from Italian cittadella, diminutive (small version) of cittade, "city", from Latin civitatem.