pilot biscuit vs hardtack

pilot biscuit and hardtack both are nouns.

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

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

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

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

pilot biscuit (noun)	hardtack (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