excretion vs expelling

excretion and expelling both are nouns.

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

As nouns, expelling is a hypernym of excretion; that is, expelling is a word with a broader meaning than excretion:

excretion: the bodily process of discharging waste matter
expelling: any of several bodily processes by which substances go out of the body

Other hypernyms of excretion include discharge, emission.

excretion (noun)	expelling (noun)
the bodily process of discharging waste matter	any of several bodily processes by which substances go out of the body
waste matter (as urine or sweat but especially feces) discharged from the body