sea biscuit vs ship biscuit

sea biscuit and ship biscuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea biscuit	Yes	No	No	No
ship biscuit	Yes	No	No	No

As nouns, sea biscuit and ship biscuit are synonyms defined as:

sea biscuit and ship biscuit: very hard unsalted biscuit or bread; a former ship's staple

Other synonyms of sea biscuit include hardtack, pilot biscuit, pilot bread.

sea biscuit (noun)	ship biscuit (noun)
very hard unsalted biscuit or bread; a former ship's staple	very hard unsalted biscuit or bread; a former ship's staple