Lose  v. (-sing; past and past part. Lost) 1 be deprived of or cease to have, esp. By negligence. 2 be deprived of (a person) by death. 3 become unable to find, follow, or understand (lose one's way). 4 let or have pass from one's control or reach (lost my chance; lost his composure). 5 be defeated in (a game, lawsuit, battle, etc.). 6 get rid of (lost our pursuers; lose weight). 7 forfeit (a right to a thing). 8 spend (time, efforts, etc.) To no purpose.