Real Dictionary

overwork
verb: If you overwork or if someone overworks you, you work too hard, and are likely to become very tired or ill.

overwork in American English
to work or use to excess
intransitive verb: to work too hard, too much, or too long; work to excess
noun: work beyond one's strength or capacity
transitive verb: to cause to work too hard, too much, or too long; weary or exhaust with work (often used reflexively)

overwork in British English
noun: excessive or excessively tiring work
verb: to work or cause to work too hard or too long