defend vs bulwark

defend is not a noun while bulwark is a noun.

Word	Noun	Adjective	Verb	Adverb
defend	No	No	Yes	No
bulwark	Yes	No	Yes	No

As verbs, bulwark is a hyponym of defend; that is, bulwark is a word with a more specific, narrower meaning than defend:

Other hyponyms of defend include protect, ward off, arrest, check, contain, hold back, stop, turn back.

defend (noun)	bulwark (noun)
	a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away
	an embankment built around a space for defensive purposes
	a fencelike structure around a deck

defend (verb)	bulwark (verb)
argue or speak in defense of	defend with a bulwark
state or assert
be on the defensive; act against an attack
protect against a challenge or attack
protect or fight for as a champion
fight against or resist strongly
be the defense counsel for someone in a trial