the shits vs diarrhea

the shits and diarrhea both are nouns.

Word	Noun	Adjective	Verb	Adverb
the shits	Yes	No	No	No
diarrhea	Yes	No	No	No

As nouns, diarrhea is a hypernym of the shits; that is, diarrhea is a word with a broader meaning than the shits:

the shits: obscene terms for diarrhea
diarrhea: frequent and watery bowel movements; can be a symptom of infection or food poisoning or colitis or a gastrointestinal tumor

Other hypernyms of the shits include diarrhoea, looseness, looseness of the bowels.

the shits (noun)	diarrhea (noun)
obscene terms for diarrhea	frequent and watery bowel movements; can be a symptom of infection or food poisoning or colitis or a gastrointestinal tumor