Longman Dictionary of Contemporary English - signal

~1 n 1 a sound or action that you make in order to give information to someone or tell them to do something  (signal (for sb) to do sth)  (A bell began to ring, the 8 o'clock signal to start work. | When he closes his book, it's a signal for everyone to stand up. | give a signal)  (Don't start yet - wait for me to give the signal. | at a signal (from sb))  (At a signal from their leader the worshippers knelt to pray. | danger signal/warning signal etc)  (A red flag is often used as a danger signal.)  (- see also smoke signal) 2 an event or action that shows what someone feels or what is likely to happen  (signal that)  (Gorbachev's speech was a signal that major changes were on the way. | a clear signal)  (The opinion poll is a clear signal that voters do not support the President's foreign policy. | danger signal/warning signal)  (Rapid breathing is a danger signal and you should call your doctor. | send/give a signal)  (This will send the wrong signal to potential investors.) 3 a series of light waves, sound waves etc that carry an image, sound, or message, such as is used in radio or television  (send out/transmit a signal (to))  (The signal was sent out to our troops immediately. | receive/pick up a signal)  (Astronomers have been picking up faint signals that may be from a distant planet.) 4 a piece of equipment with coloured lights, used on a railway to tell train drivers whether they can continue or must stop  (signal failure (=when these lights do not work))  (The report confirmed that signal failure had been the cause of the accident.) ~2 v signalled, signalling BrE, signaled, signaling AmE 1 to give a signal in order to give information or tell someone to do something + a  (Mary was signalling wildly at us, but we didn't even notice.)  (The judge signaled to a police officer and the man was led away.) + for  (He pushed his plate away and signaled for coffee.) signal (to) sb to do sth  (She was signalling to the children to stay outside.) 2 to make something clear by what you say or do  (Both sides have signaled their willingness to start negotiations.) 3 to be a sign or proof of something  (the lengthening days that signal the end of winter) ~3 adj only before noun formal important  (signal achievement/success/failure etc)  (Getting the health care bill passed was a signal personal triumph for the President.)