dejection vs melaena

dejection and melaena both are nouns.

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

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

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

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

dejection (noun)	melaena (noun)
a state of melancholy depression	abnormally dark tarry feces containing blood (usually from gastrointestinal bleeding)
solid excretory product evacuated from the bowels