The Collaborative International Dictionary of English v.0.48:
Alka-seltzer \Alka-seltzer\ n. 1. a commerical antacid; -- the tablets dissolve in water to give an effervescent solution. [trademark] WordNet 1.5]WordNet (r) 3.0 (2006):
Alka-seltzer n 1: a commercial antacid that contains aspirin; tablets dissolve in water to give an effervescent solution