faecal matter vs excretion

faecal matter and excretion both are nouns.

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

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

faecal 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 faecal matter include body waste, excrement, excreta, excretory product.

faecal 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