Entry 1 sense Webster, 1913 Antacid /(ănt*ăs"ĭd)/ · Ant·ac·id · IPA /ænˈtæsɪd/ 01 n. A remedy for acidity of the stomach, as an alkali or absorbent. 1. A remedy for acidity of the stomach, as an alkali or absorbent.(Med.)