on the lookout

Idioms  

1. 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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Example Sentences

They will also be on the lookout for possible flashes of light caused by meteorites crashing into the surface of the Moon.

From Barron's • Apr. 5, 2026

Be on the lookout for anything that seems too good to be true.

From MarketWatch • Mar. 30, 2026

Despite the misgivings of the scientific community, longevity enthusiasts like Scott and Chitwood are always on the lookout for the next therapy to try.

From Slate • Mar. 30, 2026

Her daughters — artists Alison and Lezley, and writer Tracye, their mother’s studio director — also stay on the lookout for objects that might catch her eye.

From Los Angeles Times • Feb. 20, 2026

He should have been on the lookout for that; but the lucky thing was that he knew that Britten had done all his tricks at once, had shot his bolt, had played all his cards.

From "Native Son" by Richard Wright

Related Words

• active
• bright
• careful
• intelligent
• observant
• perceptive
• sharp
• vigilant
• wary
• watchful
• wired
• wise