waste matter vs excreta

waste matter and excreta both are nouns.

Word	Noun	Adjective	Verb	Adverb
waste matter	Yes	No	No	No
excreta	Yes	No	No	No

As nouns, excreta is a hyponym of waste matter; that is, excreta is a word with a more specific, narrower meaning than waste matter:

waste matter: any materials unused and rejected as worthless or unwanted
excreta: waste matter (as urine or sweat but especially feces) discharged from the body

waste matter (noun)	excreta (noun)
any materials unused and rejected as worthless or unwanted	waste matter (as urine or sweat but especially feces) discharged from the body