If someone overachieves in something such as school work or a job, they work very hard, especially in a way that makes them tired or unhappy. They want to be successful because it is very important to them to do well and not because they enjoy what they are doing. emotions such as guilt, compulsion to please or overachieve, or depression. + overachiever overachievers over·achiev·er He comes from a family of overachievers