feces vs melaena

feces and melaena both are nouns.

Word	Noun	Adjective	Verb	Adverb
feces	Yes	No	No	No
melaena	Yes	No	No	No

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

feces: solid excretory product evacuated from the bowels
melaena: abnormally dark tarry feces containing blood (usually from gastrointestinal bleeding)

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

feces (noun)	melaena (noun)
solid excretory product evacuated from the bowels	abnormally dark tarry feces containing blood (usually from gastrointestinal bleeding)