brainiac vs prodigy

brainiac and prodigy both are nouns.

Word	Noun	Adjective	Verb	Adverb
brainiac	Yes	No	No	No
prodigy	Yes	No	No	No

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

brainiac: someone who has exceptional intellectual ability and originality
prodigy: an unusually gifted or intelligent (young) person; someone whose talents excite wonder and admiration

brainiac (noun)	prodigy (noun)
someone who has exceptional intellectual ability and originality	an impressive or wonderful example of a particular quality
	a sign of something about to happen
	an unusually gifted or intelligent (young) person; someone whose talents excite wonder and admiration