n. phr. A slight glance; a quick look. The substitute teacher could see with half an eye that she was going to have trouble with the class. While Mary was cooking she kept half an eye on the baby to see that he didn't get into mischief.
HALF AN EYE
Meaning of HALF AN EYE in English
American idioms English vocabulary. Английский словарь американских идиом. 2012