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Dictionary.com

on alert

ADJECTIVE
on call
Synonyms
WEAK
accessible at hand at one's beck and call at one's disposal at one's fingertip available handy night call on deck on-the-spot prepared standing by within reach
ADJECTIVE
vigilant
Synonyms
STRONGEST
anxious attentive aware cautious circumspect keen observant wary
WEAK
acute agog alert guarded looking for looking to on guard on the ball on the job on the lookout on the qui vive on toes open-eyed sharp sleepless unsleeping waiting on wakeful wide-awake with eyes peeled with weather eye open
Antonyms
STRONGEST
careless heedless ignorant inattentive incautious indifferent indiscreet rash thoughtless unaware uncareful unobservant
WEAK
impulsive negligent

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.

The Soviet foreign minister, Andrei Gromyko, observed at the time: “Americans put forces on alert so often that it is hard to know what it means.”

From Slate • Apr. 21, 2026

The IMF chief said regulators should be on alert for any signs of instability in the financial system as a consequence of the conflict.

From The Wall Street Journal • Apr. 9, 2026

On Sunday morning internal health service communications went out across Kent and Medway informing services of the outbreak, so NHS 111, local A&Es and GPs were on alert for cases.

From BBC • Mar. 24, 2026

Doncic picked up his 15th technical foul of the season against Denver on March 5, putting him on alert for a possible suspension.

From Los Angeles Times • Mar. 22, 2026

Lately, I felt like I always had to be on alert for the next raccoon invasion.

From "Crenshaw" by Katherine Applegate