bastion vs kremlin

bastion and kremlin both are nouns.

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

As nouns, kremlin is a hyponym of bastion; that is, kremlin is a word with a more specific, narrower meaning than bastion:

bastion: a stronghold into which people could go for shelter during a battle
kremlin: citadel of a Russian town

Other hyponyms of bastion include acropolis.

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