excreting vs expelling

excreting and expelling both are nouns.

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

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

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

Other hypernyms of excreting include discharge, emission.

excreting (noun)	expelling (noun)
the bodily process of discharging waste matter	any of several bodily processes by which substances go out of the body