fecal matter vs BM

fecal matter and BM both are nouns.

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

As nouns, fecal matter and BM are synonyms defined as:

Other synonyms of fecal matter include dejection, faecal matter, faeces, feces, ordure, stool.

fecal matter (noun)	BM (noun)
solid excretory product evacuated from the bowels	solid excretory product evacuated from the bowels