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Definitions

on the alert

ADJECTIVE
unsleeping
Synonyms
WEAK
alive astir attentive awake careful heedful insomniac insomnious observant on guard on the lookout on the qui vive sleepless vigilant waking wary watchful wide-awake
ADJECTIVE
wakeful
Synonyms
WEAK
alive astir attentive careful heedful insomniac insomnious observant on guard on the lookout on the qui vive sleepless unsleeping vigilant waking wary watchful wide-awake
Antonyms
WEAK
sleepy unaware

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

It’s a play on the alert that heralded a new participant in online chat rooms of the 1990s and aughts, a time when many of this phrase’s current users weren’t born.

From The Wall Street Journal • Oct. 16, 2025

Motorists have been warned to be on the alert for scammers posing as car finance lenders offering fake compensation.

From BBC • Aug. 11, 2025

The intelligence community is on the alert for spies looking to penetrate America’s commercial space sector through cyberattacks and strategic investments to gain access to critical networks.

From Washington Times • Aug. 22, 2023

China also returns from a holiday on Monday, with markets on the alert for further support measures from Beijing to stimulate the country's faltering economic recovery.

From Reuters • Jun. 26, 2023

Fortunately, Scragg the weasel was on the alert.

From "Redwall" by Brian Jacques