earthwork vs bulwark

earthwork and bulwark both are nouns.

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

As nouns, bulwark is a hypernym of earthwork; that is, bulwark is a word with a broader meaning than earthwork:

Other hypernyms of earthwork include rampart, wall.

earthwork (noun)	bulwark (noun)
an earthen rampart	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

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