Noah Webster's New International Dictionary of the English Language

1. (n.) A sign made for the purpose of giving notice to a person of some occurrence, command, or danger; also, a sign, event, or watchword, which has been agreed upon as the occasion of concerted action.

2. (n.) A token; an indication; a foreshadowing; a sign.

3. (a.) Noticeable; distinguished from what is ordinary; eminent; remarkable; memorable; as, a signal exploit; a signal service; a signal act of benevolence.

4. (a.) of or pertaining to signals, or the use of signals in conveying information; as, a signal flag or officer.

5. (v. t.) To communicate by signals; as, to signal orders.

6. (v. t.) To notify by a signals; to make a signal or signals to; as, to signal a fleet to anchor.