To overwork means to work too hard or too long, pushing yourself beyond what's healthy or sustainable. When you overwork, you keep going even after your brain and body are telling you to rest. A student who stays up until midnight finishing homework, then wakes at dawn to study more, then spends lunch period working on a project is overworking. A parent who works a full-time job, cares for the family, volunteers at school, and never takes time to relax is overworking.

Overwork means working so much that it leaves you exhausted, irritable, and unable to think clearly. It's when someone works so much that the quality of their work actually gets worse, not better. Working hard on something you care about can feel energizing and satisfying, but overwork drains you instead. A writer who stays at her desk for twelve hours straight might make more careless mistakes than if she had taken breaks. An athlete who practices intensely every single day without rest becomes more likely to get injured.

The noun form is overwork as well: “Too much overwork made him sick.” People also use the past participle overworked as an adjective: “The overworked teacher graded papers late into the night.”