meconium vs fecal matter

meconium and fecal matter both are nouns.

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

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

meconium: thick dark green mucoid material that is the first feces of a newborn child
fecal matter: solid excretory product evacuated from the bowels

Other hypernyms of meconium include BM, dejection, faecal matter, faeces, feces, ordure, stool.

meconium (noun)	fecal matter (noun)
thick dark green mucoid material that is the first feces of a newborn child	solid excretory product evacuated from the bowels