fecal matter vs excreta

fecal matter and excreta both are nouns.

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

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

fecal 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 fecal matter include body waste, excrement, excretion, excretory product.

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