know (someone or something) by sight(redirected from know it by sight)
know (someone or something) by sight
To recognize someone or something based solely on appearance (without knowing any other information, such as a name, etc.). Even after working there for a year, there were still some co-workers I only knew by sight. I'd know the place by sight, but I don't think I could tell you how to get there.
know someone by sight
to recognize a person's face, but not know the name. I'm afraid I don't know her by sight. I know all my employees by sight.
know by sight
Recognize someone or something by appearance but not know the name or other details. For example, I know a lot of people by sight from the tennis courts. [1200s]