a ‧ chiev ‧ er /əˈtʃiːvə $ -ər/ BrE AmE noun [countable]
[ Word Family: noun : ↑ achievement , ↑ achiever , ↑ underachiever ≠ OVERACHIEVER , ↑ underachievement ≠ OVERACHIEVEMENT ; verb : ↑ achieve , ↑ underachieve ≠ OVERACHIEVE ; adjective : ↑ achievable ]
someone who is successful because they are determined and work hard ⇨ underachiever , overachiever