bathyal zone vs seabed

bathyal zone and seabed both are nouns.

Word	Noun	Adjective	Verb	Adverb
bathyal zone	Yes	No	No	No
seabed	Yes	No	No	No

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

bathyal zone: the steep descent of the seabed from the continental shelf to the abyssal zone
seabed: the bottom of a sea or ocean

Other hypernyms of bathyal zone include Davy Jones's locker, Davy Jones, ocean bottom, ocean floor, sea bottom, sea floor.

bathyal zone (noun)	seabed (noun)
the steep descent of the seabed from the continental shelf to the abyssal zone	the bottom of a sea or ocean