1. To hold, place, or keep someone or something behind someone or something else. In this usage, a noun or pronoun can be used between "keep" and "behind." Keep the gifts behind your back so we can surprise her with them.
2. To stay in back of someone or something. Kids, make sure to keep behind the grown-ups on our walk.
3. To require a student to repeat a grade of school. In this usage, a noun or pronoun can be used between "keep" and "behind." Am I really being kept behind? I don't want to repeat junior year—can't I go to summer school or something?
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
1. To hold or maintain someone or something to the rear of something else: I keep my car behind the garage.
2. To remain to the rear of something: We didn't want them to see us, so we kept behind the barn when they arrived.
3. To fail to advance someone to the next grade or class of school; flunk. Usually used in the passive: After a year of doing poorly in class, the troubled student was kept behind.
The American Heritage® Dictionary of Phrasal Verbs. Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.