bulwark vs earthwork

bulwark and earthwork both are nouns.

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

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

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

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

bulwark (verb)	earthwork (verb)
defend with a bulwark