A hard, dry biscuit made from flour and water, historically used as long-lasting food for sailors and soldiers.
Compound of 'hard' plus 'tack' (nautical slang for food), from 17th century naval terminology; 'tack' possibly from Old Norse 'taka' meaning 'to take or seize.'
Hardtack was the ultimate survival food—so hard it could chip teeth and so preserved by being essentially moisture-free that biscuits from Nelson's navy were discovered in shipwrecks centuries later, still theoretically edible.
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