1. to tell someone about a possible danger, problem, or other unpleasant thing that might happen
Usage: third person singular present tense of ‘warn’
2. to tell someone that they will be punished if they continue to behave in a particular way
Usage: third person singular present tense of ‘warn’

Examples

• The weather service warns of severe storms tonight.
• She warns her children about talking to strangers.
• The sign warns drivers of the sharp curve ahead.
• The teacher warns students about cheating on tests.
• He warns that prices will increase next month.
• The doctor warns patients about the side effects.
• The lifeguard warns swimmers about strong currents.