Definitions:

1. condition of heightened watchfulness or preparation for action noun
   • bombers were put on alert during the crisis
2. engaged in or accustomed to close observation adjective
   • caught by a couple of alert cops
3. mentally perceptive and responsive adjective
   • an alert mind
4. to warn or arouse to a sense of danger or call to a state of preparedness verb
   • I alerted them of the impending storm.

Synonyms:

• alarm
• alarum
• alerting
• alive
• awake
• qui vive
• rattling
• warning signal
• watchful

NearBy Words:

• alerting
• alertly
• alertness