know (someone or something) by sight(redirected from knows by sight)
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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]