continental shelf vs seabed

continental shelf and seabed both are nouns.

Word	Noun	Adjective	Verb	Adverb
continental shelf	Yes	No	No	No
seabed	Yes	No	No	No

As nouns, seabed is a hypernym of continental shelf; that is, seabed is a word with a broader meaning than continental shelf:

continental shelf: the relatively shallow (up to 200 meters) seabed surrounding a continent
seabed: the bottom of a sea or ocean

Other hypernyms of continental shelf include Davy Jones's locker, Davy Jones, ocean bottom, ocean floor, sea bottom, sea floor.

continental shelf (noun)	seabed (noun)
the relatively shallow (up to 200 meters) seabed surrounding a continent	the bottom of a sea or ocean