Definition & Meaning of "[give] {sb} the (glad|) eye"

What is the origin of the idiom "give someone the eye" and when to use it?

The phrase "give someone the eye" originated in the early 20th century and is rooted in the observation that eye contact and non-verbal cues can be powerful means of communication, particularly in expressing romantic or sexual interest. It is used to describe the act of looking at someone with a suggestive or flirtatious intent. It implies using eye contact and body language to express attraction or interest in a subtle or playful manner.