knock something off

Từ điển Oxford Advanced Learner 8th

▪ I. ˌknock sthˈoff derived
1. (informal)to complete sth quickly and without much effort
•He knocks off three novels a year.
2. (BrE, slang)to steal sth; to steal from a place
•to knock off a DVD player
•to knock off a bank
Main entry: ↑knock_derived
 
▪ II. ˌknock sthˈoff | ˌknock sthˈoff sth derived
(informal)to reduce the price or value of sth
•They knocked off $60 because of a scratch.
•The news knocked 13% off the company's shares.
Main entry: ↑knock_derived