An agent that counteracts or neutralizes acidity (especially in the stomach); SYN. gastric antacid, alkalizer.
Any substance that neutralizes stomach acid, such as sodium bicarbonate or magnesium hydroxide (“milk of magnesia”).
Antacids are weak bases, swallowed as solids or emulsions. They may be taken between meals to relieve symptoms of hyperacidity, such as pain, bloating, nausea, and “heartburn”. Excessive or prolonged need for antacids should be investigated medically.

Curative of acidity, especially intestinal.
Acting to neutralize acid (especially in the stomach).