An under achiever is one who is capable to doing more or better than he does.
He does not use all of his tools. For example a Baseball player might be able to steal bases and help his team, but it's too much bother and he can make the team without stealing any bases.
Under achiever
Upalabdhiyāṁ
patrator
There is no slang word for the word over achiever per-say but they can be referred to as things like goody too shoes or stuck up.
Anover achiever is some one who tries too hard to get things
under the moon
under
Sub rosa, meaning "under the rose."
whether or not the African American achiever is still alive
over
Subterranean.
The Hero Achiever is a motorcycle manufactured by Honda. It is currently available in India, and offers a top speed of 101kph. In India, the Hero Achiever costs Rs. 61,000.