cream of tartar; potassium hydrogen tartrate
Technical term for the potassium acid salt of tartaric acid, used in cooking and chemistry.
Cream of tartar is used as an ingredient in baking powder.
Compound of 酒石 (しゅせき, 'tartar') and 英 (えい, here likely an abbreviation or phonetic element). The exact derivation of 英 is uncertain; it may be ateji or a historical abbreviation.