sea bottom vs Davy Jones's locker

sea bottom and Davy Jones's locker both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea bottom	Yes	No	No	No
Davy Jones's locker	Yes	No	No	No

As nouns, sea bottom and Davy Jones's locker are synonyms defined as:

Other synonyms of sea bottom include Davy Jones, ocean bottom, ocean floor, sea floor, seabed.

sea bottom (noun)	Davy Jones's locker (noun)
the bottom of a sea or ocean	the bottom of a sea or ocean