indigestion vs stomach upset

indigestion and stomach upset both are nouns.

Word	Noun	Adjective	Verb	Adverb
indigestion	Yes	No	No	No
stomach upset	Yes	No	No	No

As nouns, indigestion and stomach upset are synonyms defined as:

indigestion and stomach upset: a disorder of digestive function characterized by discomfort or heartburn or nausea

Other synonyms of indigestion include dyspepsia, upset stomach.

indigestion (noun)	stomach upset (noun)
a disorder of digestive function characterized by discomfort or heartburn or nausea	a disorder of digestive function characterized by discomfort or heartburn or nausea