bastion vs citadel

bastion and citadel both are nouns.

Word	Noun	Adjective	Verb	Adverb
bastion	Yes	No	No	No
citadel	Yes	No	No	No

As nouns, bastion and citadel are synonyms defined as:

bastion and citadel: a stronghold into which people could go for shelter during a battle

bastion (noun)	citadel (noun)
projecting part of a rampart or other fortification	a stronghold into which people could go for shelter during a battle
a stronghold into which people could go for shelter during a battle
a group that defends a principle