Etymology: probably so called from its being the choicest or most essential ingredient in tartar
: a white crystalline salt KHC 4 H 4 O 6 with a pleasant acid taste found in grapes and in tartars from wine making, prepared especially from argols and also synthetically from tartaric acid, and used chiefly in foods (as baking powder and hard candy) and in certain treatments of metals (as in the electrolytic tinning of iron and steel); potassium hydrogen tartrate — called also potassium acid tartrate, potassium bitartrate