Bromo-seltzer vs antiacid

Bromo-seltzer and antiacid both are nouns.

Word	Noun	Adjective	Verb	Adverb
Bromo-seltzer	Yes	No	No	No
antiacid	Yes	No	No	No

As nouns, antiacid is a hypernym of Bromo-seltzer; that is, antiacid is a word with a broader meaning than Bromo-seltzer:

Bromo-seltzer: an antacid
antiacid: an agent that counteracts or neutralizes acidity (especially in the stomach)

Other hypernyms of Bromo-seltzer include alkaliser, alkalizer, antacid, gastric antacid.

Bromo-seltzer (noun)	antiacid (noun)
an antacid	an agent that counteracts or neutralizes acidity (especially in the stomach)