underperformer vs underachiever

underperformer and underachiever both are nouns.

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

As nouns, underperformer and underachiever are synonyms defined as:

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

Other synonyms of underperformer include nonachiever.

underperformer (noun)	underachiever (noun)
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
a student who does not perform as well as expected or as well as the IQ indicates