hardtack vs pilot biscuit

hardtack and pilot biscuit both are nouns.

Word	Noun	Adjective	Verb	Adverb
hardtack	Yes	No	No	No
pilot biscuit	Yes	No	No	No

As nouns, hardtack and pilot biscuit are synonyms defined as:

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

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

hardtack (noun)	pilot biscuit (noun)
very hard unsalted biscuit or bread; a former ship's staple	very hard unsalted biscuit or bread; a former ship's staple
a mountain mahogany