gastroenteritis vs stomach flu

gastroenteritis and stomach flu both are nouns.

Word	Noun	Adjective	Verb	Adverb
gastroenteritis	Yes	No	No	No
stomach flu	Yes	No	No	No

As nouns, gastroenteritis and stomach flu are synonyms defined as:

gastroenteritis and stomach flu: inflammation of the stomach and intestines; can be caused by Salmonella enteritidis

Other synonyms of gastroenteritis include intestinal flu.

gastroenteritis (noun)	stomach flu (noun)
inflammation of the stomach and intestines; can be caused by Salmonella enteritidis	inflammation of the stomach and intestines; can be caused by Salmonella enteritidis