warn

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To make aware in advance of actual or potential harm, danger, or evil.
2. v. To admonish as to action or manners.
3. v. To notify (a person) to go or stay away: warned them off the posted property.
4. v. To notify or apprise in advance: They called and warned me that they might be delayed.
5. v. To give a warning.

Century Dictionary and Cyclopedia

1. n. A denial; refusal.
2. To put on guard by timely notice; wake, ware, or give notice to beforehand, as of approaching danger or of something to be avoided or guarded against; caution; admonish; tell or command admonishingly; advise.
3. To admonish, as to any duty; advise; ex postulate with.
4. To apprise; give notice to; make ware or aware; inform previously; notify; direct; bid; summon.
5. To deny; refuse; forbid.
6. To defend; keep or ward off.

Wiktionary

1. v. intransitive To give warning.
2. v. obsolete To refuse, deny (someone something).

GNU Webster's 1913

1. v. obsolete To refuse.
2. v. To make ware or aware; to give previous information to; to give notice to; to notify; to admonish; hence, to notify or summon by authority
3. v. To give notice to, of approaching or probable danger or evil; to caution against anything that may prove injurious.
4. v. obsolete To ward off.

WordNet 3.0

1. v. admonish or counsel in terms of someone's behavior
2. v. notify, usually in advance
3. v. notify of danger, potential harm, or risk
4. v. ask to go away