kosher [M19th] Only food that is kosher may be eaten by Orthodox Jews. Animals must be slaughtered and prepared in the prescribed way, meat and milk must not be cooked or consumed together, and certain creatures, notably pigs and shellfish, are forbidden altogether. The word is from Hebrew kāsēr ‘right, proper’, and was first used in English in the mid 19th century—the slang sense, ‘genuine and legitimate’, is almost as old, going back to the 1880s.