signal1

noun

• 1a gesture, action, or sound that is used to convey information or instructions, typically by prearrangement between the parties concerned:the firing of the gun was the signal for a chain of beacons to be lit [with infinitive]:the policeman raised his hand as a signal to stop
• an indication of a situation:the markets are waiting for a clear signal about the direction of policy
• an event or statement that provides the impulse for an occurrence:the champion’s announcement that he was retiring was the signal for scores of journalists to gather at his last match
• Bridge a prearranged convention of bidding or play intended to convey information to one’s partner.

• 2an electrical impulse or radio wave transmitted or received:equipment for receiving TV signals

• 3an apparatus on a railway, typically a coloured light or a semaphore, giving indications to train drivers of whether or not the line is clear: the driver of the mail train overran a signal at danger and ran into the rear of an express

verb (signals, signalling, signalled; US signals, signaling, signaled)

• convey information or instructions by means of a gesture, action, or sound:hold your fire until I signal
• [with object and infinitive] instruct (someone) to do something by means of gestures or signs:she signalled Charlotte to be silent
• (of a cyclist, motorist, or vehicle) indicate an intention to turn in a specified direction using an extended arm or flashing indicator: [with complement]:Stone signalled right [with infinitive]:the truck signalled to turn left
• [with object] indicate the existence or occurrence of (something) by actions or sounds:the Community could signal displeasure by refusing to cooperate [with clause]:she gave a glance which signalled that her father was being secretive