To give warning signs of (impending peril)
To caution is defined as to warn.
To caution against specific faults; warn
To tell (a person) of a danger, coming evil, misfortune, etc.; put on guard; caution
To serve as an omen of; betoken:
To send (a message) by signaling
The definition of alarm is to warn of danger or to make someone afraid or distressed.
Threaten is defined as to pose a danger to someone or something, or to make someone believe you pose a danger by making statements indicating an intent to harm them.
To foresee or forecast
Find another word for forewarn. In this page you can discover 17 synonyms, antonyms, idiomatic expressions, and related words for forewarn, like: alert, forebode, foresight, caution, admonish, warn, augur, flag, notify, portend and signal.