keep an eye on, to

keep an eye on someone or something

 and have an eye on someone or something; keep one's eye(s) on someone or something; have one's eye on someone or something
Fig. to watch someone or something; to monitor someone or something closely. I have my eye on the apple tree. When the apples ripen, I'll harvest them. Please keep an eye on the baby. Will you please keep your eye on my house while I'm on vacation?
See also: eye, keep, on
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.

keep an eye on

1. To watch over attentively; mind.
2. To watch closely or carefully: keep your eye on the ball.
See also: eye, keep, on
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

keep an eye on, to

To keep watch over something or someone. See also eye for/to the main chance; keep your eyes. . .
See also: eye, keep
The Dictionary of Clichés by Christine Ammer Copyright © 2013 by Christine Ammer
See also: