What is the meaning of signal?

noun

• Any nonverbal action or gesture that encodes a message.
  • usage: "signals from the boat suddenly stopped"
  • synonyms: signaling, sign
• Any incitement to action.
  • usage: "he awaited the signal to start"; "the victory was a signal for wild celebration"
• An electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes.

verb

• Communicate silently and non-verbally by signals or signs.
  • usage: "He signed his disapproval with a dismissive hand gesture"; "The diner signaled the waiters to bring the menu"
  • synonyms: sign, signalize, signalise
• Be a signal for or a symptom of.
  • usage: "These symptoms indicate a serious illness"; "Her behavior points to a severe neurosis"; "The economic indicators signal that the euro is undervalued"
  • synonyms: bespeak, betoken, indicate, point

adjective

• Notably out of the ordinary.
  • usage: "the year saw one signal triumph for the Labour party"