keep somebody back

Từ điển Oxford Advanced Learner 8th

▪ I. ˌkeep sbˈback derived
1. (BrE) (NAmE ˌkeep sb ˈafter)to make a student stay at school after normal hours as a punishment
2. (NAmE)to make a student repeat a year at school because of poor marks/grades
Main entry: ↑keep_derived
 
▪ II. ˌkeep sbˈback (from sb/sth) derived
to make sb stay at a distance from sb/sth
•Barricades were erected to keep back the crowds.
Main entry: ↑keep_derived