hematemesis vs emesis

hematemesis and emesis both are nouns.

Word	Noun	Adjective	Verb	Adverb
hematemesis	Yes	No	No	No
emesis	Yes	No	No	No

As nouns, emesis is a hypernym of hematemesis; that is, emesis is a word with a broader meaning than hematemesis:

hematemesis: vomiting blood
emesis: the reflex act of ejecting the contents of the stomach through the mouth

Other hypernyms of hematemesis include disgorgement, puking, regurgitation, vomit, vomiting.

hematemesis (noun)	emesis (noun)
vomiting blood	the reflex act of ejecting the contents of the stomach through the mouth