faecal matter vs excreta

faecal matter and excreta both are nouns.

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

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

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

Other hypernyms of faecal matter include body waste, excrement, excretion, excretory product.

faecal matter (noun)	excreta (noun)
solid excretory product evacuated from the bowels	waste matter (as urine or sweat but especially feces) discharged from the body