BM vs meconium

BM and meconium both are nouns.

Word	Noun	Adjective	Verb	Adverb
BM	Yes	No	No	No
meconium	Yes	No	No	No

As nouns, meconium is a hyponym of BM; that is, meconium is a word with a more specific, narrower meaning than BM:

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

Other hyponyms of BM include dog do, dog shit, dog turd, doggy do, crap, dirt, poop, shit, shite, turd, droppings, dung, muck, melaena, melena.

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