What does "underachiever" mean?

One who underachieves, i.e. performs less well than expected.

Underachiever

Common synonyms include: underperformer, bookworm, chokers, disappointing student, failure, flunks.

noun

noun ·5 syllables ·Rare ·Advanced level

Noun

1
One who underachieves, i.e. performs less well than expected.
"Woody Allen has provided what is probably the best theological answer to the problem of evil: God is not evil; He is just an underachiever."
2
a student who does not perform as well as expected or as well as the IQ indicates wordnet

"Tom has been an underachiever all his life."

From underachieve + -er or under- + achiever.