I am wondering why there is just one eye in the idiom of 'Beauty is in the eye of the beholder'? I mean why eye is in singular, normally, a person has two eyes.
Interestingly, I was wondering about that too. There are more expressions that involve one eye only. For example, "To keep an eye on somebody, something." I have no the scientific explanation but what I think is that the "eye" is used figuratively as a definition of the close attention, of one's particular interest in the subject. Does it make sense?
By the way, when I translated from Russian a poem by Sergey Yesenin (I am by no mean a professional), I tried and made a nonce-word based on the "one eye" idiom.
"So long, with no word, nor hugging.
Don't cry and don't grieve your eye."
And I was trying to say (well, the author, Yesenin, was trying to say): "Don't frown your eyebrows in grief."
Does this make sense to a native ear? (See???? Same thing!!!! We have TWO ears and still we say "to a foreigner ear". It does sound like we use such expressions figuratively.)