fecal matter vs excretion

fecal matter and excretion both are nouns.

Word	Noun	Adjective	Verb	Adverb
fecal matter	Yes	No	No	No
excretion	Yes	No	No	No

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

fecal matter: solid excretory product evacuated from the bowels
excretion: waste matter (as urine or sweat but especially feces) discharged from the body

Other hypernyms of fecal matter include body waste, excrement, excreta, excretory product.

fecal matter (noun)	excretion (noun)
solid excretory product evacuated from the bowels	the bodily process of discharging waste matter
	waste matter (as urine or sweat but especially feces) discharged from the body