warn

The word “warn” means to alert someone to a danger, problem, or something unpleasant that may happen. In plain terms, to tell someone about a danger or problem ahead of time so they can avoid it.

“Warn” is pronounced WAWN (/ˈwɔɹn/ in IPA).

Here is “warn” used in a sentence: “The forecast warned residents of an approaching storm.”

“Warn” is a verb.

The word “warn” comes from Old English. From Old English warnian ("to take heed, to warn"), from a Germanic root meaning "to be aware" or "give heed.".

“Warn” is a fairly common word in modern English, usually learned at around the B1 level.

“Warn” has 2 distinct senses listed in this dictionary. The most common is: to alert someone to a danger, problem, or something unpleasant that may happen.

All three prepositions are correct, with different shades. You warn someone of or about a danger or problem, with of sounding slightly more formal, and you warn someone against an action you are advising them not to take. Warn can also be followed by an object and an infinitive: "she warned him to stay away".

Both mean to alert someone to possible danger or advise them against a course of action, but caution is milder and more formal, often appearing in official contexts. Warn is the everyday word and tends to suggest more serious or urgent danger.

To warn someone is to alert them to a danger or problem so they can avoid harm; the speaker's intent is protective. To threaten is to declare that you yourself will cause the harm. "I'm warning you" sits on the boundary, since it is often a veiled threat.

Both mean to alert someone to a coming danger or problem, but forewarn stresses that the alert comes well in advance, as in the proverb "forewarned is forearmed". Warn is the general-purpose word; forewarn is slightly more formal and literary.