very hard unsalted biscuit or bread; a former ship's staple
同义词：pilot biscuit, pilot bread, sea biscuit, ship biscuit
a mountain mahogany
hardtack详细解释
hard.tack n.（名词）A hard biscuit or bread made with only flour and water.Also called sea biscuit ,sea bread ,ship biscuit 硬饼干：仅用面粉和水制成的硬饼干或面包也作 sea biscuit,sea bread,ship biscuit
