on the lookout

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Idioms and Phrases

Also, on the watch . Vigilant, alert, as in Be on the lookout for the twins—they're somewhere on this playground , or He was on the watch for her arrival . Both phrases were originally used with upon . Upon the lookout was originally nautical usage, meaning “on duty being watchful” (as for another ship, rocks, or land); it appeared in the mid-1700s, and on replaced upon about a century later. Upon the watch was first recorded in Daniel Defoe's Robinson Crusoe (1719), and on the watch in Jane Austen's Sense and Sensibility (1797).

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Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

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