signal

(noun) any nonverbal action or gesture that encodes a message. Synonyms: signaling, sign. Example: "Signals from the boat suddenly stopped."

(noun) any incitement to action. Examples: "He awaited the signal to start." "The victory was a signal for wild celebration."

(noun) 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. Synonyms: sign, signalize, signalise. Examples: "He signed his disapproval with a dismissive hand gesture." "The diner signaled the waiters to bring the menu."

(verb) be a signal for or a symptom of. Synonyms: bespeak, betoken, indicate, point. Examples: "These symptoms indicate a serious illness." "Her behavior points to a severe neurosis." "The economic indicators signal that the euro is undervalued."

(adj) notably out of the ordinary. Example: "The year saw one signal triumph for the labour party."