megaloblast vs red blood cell

megaloblast and red blood cell both are nouns.

Word	Noun	Adjective	Verb	Adverb
megaloblast	Yes	No	No	No
red blood cell	Yes	No	No	No

As nouns, red blood cell is a hypernym of megaloblast; that is, red blood cell is a word with a broader meaning than megaloblast:

megaloblast: abnormally large red blood cell present in pernicious anemia and folic acid deficiency
red blood cell: a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus

Other hypernyms of megaloblast include erythrocyte, RBC.

megaloblast (noun)	red blood cell (noun)
abnormally large red blood cell present in pernicious anemia and folic acid deficiency	a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus