excretion vs shitting

excretion and shitting both are nouns.

Word	Noun	Adjective	Verb	Adverb
excretion	Yes	No	No	No
shitting	Yes	No	No	No

As nouns, shitting is a hyponym of excretion; that is, shitting is a word with a more specific, narrower meaning than excretion:

Other hyponyms of excretion include defecation, laxation, incontinence, incontinency, micturition, urination.

excretion (noun)	shitting (noun)
the bodily process of discharging waste matter	the elimination of fecal waste through the anus
waste matter (as urine or sweat but especially feces) discharged from the body