tummy vs viscus

tummy and viscus both are nouns.

Word	Noun	Adjective	Verb	Adverb
tummy	Yes	No	No	No
viscus	Yes	No	No	No

As nouns, viscus is a hypernym of tummy; that is, viscus is a word with a broader meaning than tummy:

tummy: an enlarged and muscular saclike organ of the alimentary canal; the principal organ of digestion
viscus: a main organ that is situated inside the body

Other hypernyms of tummy include internal organ.

tummy (noun)	viscus (noun)
an enlarged and muscular saclike organ of the alimentary canal; the principal organ of digestion	a main organ that is situated inside the body
slang for a paunch