sig·nal¹ / ˈsignəl/ • n. 1. a 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 | the policeman raised his hand as a signal to stop. ∎  an indication of a state of affairs: the markets are waiting for a clear signal about the direction of policy. ∎  an event or statement that provides the impulse or occasion for something specified to happen: the champion's announcement that he was retiring was the signal for scores of journalists to gather at his last match. ∎  an apparatus on a railroad, typically a colored light or a semaphore, giving indications to train engineers of whether or not the line is clear. ∎  Bridge a prearranged convention of bidding or play intended to convey information to one's partner.2. an electrical impulse or radio wave transmitted or received: equipment for receiving TV signals.• v. (-naled, -nal·ing; chiefly Brit. -nalled, -nal·ling) [intr.] transmit information or instructions by means of a gesture, action, or sound: hold your fire until I signal. ∎  [tr.] instruct (someone) to do something by means of gestures or signs rather than explicit orders: she signaled 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: Stone signaled right | the truck signaled to turn left. ∎  [tr.] indicate the existence or occurrence of (something) by actions or sounds: they could signal displeasure by refusing to cooperate. ∎  give an indication of a state of affairs: she gave a glance that signaled that her father was being secretive.DERIVATIVES: sig·nal·er n.sig·nal² • adj. striking in extent, seriousness, or importance; outstanding: he attacked the administration for its signal failure of leadership.DERIVATIVES: sig·nal·ly adv.