expelling vs excretion

expelling and excretion both are nouns.

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

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

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

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