bulwark vs battlement

bulwark and battlement both are nouns.

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

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

bulwark: an embankment built around a space for defensive purposes
battlement: a rampart built around the top of a castle with regular gaps for firing arrows or guns

Other hyponyms of bulwark include bailey, crenelation, crenellation, earthwork, fraise, merlon.

bulwark (noun)	battlement (noun)
a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away	a rampart built around the top of a castle with regular gaps for firing arrows or guns
an embankment built around a space for defensive purposes
a fencelike structure around a deck

bulwark (verb)	battlement (verb)
defend with a bulwark