underachiever vs underperformer

underachiever and underperformer both are nouns.

Word	Noun	Adjective	Verb	Adverb
underachiever	Yes	No	No	No
underperformer	Yes	No	No	No

As nouns, underachiever and underperformer are synonyms defined as:

underachiever and underperformer: a student who does not perform as well as expected or as well as the IQ indicates

Other synonyms of underachiever include nonachiever.

underachiever (noun)	underperformer (noun)
a student who does not perform as well as expected or as well as the IQ indicates	a business that is less successful than expected
	a student who does not perform as well as expected or as well as the IQ indicates