on sight

on sight idiom
Also, at sight. Immediately upon seeing, as in The soldiers threatened to shoot looters on sight, or He's able to multiply those three-digit figures at sight. [Second half of 1400s]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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