—signal /ˈsɪɡ.nəl/
adjective [before noun] FORMAL
► F0 noticeable and unusual: » a signal success/failureThesaurus+: ↑Unique and unusual , ↑Good, better and best in terms of qualitynoun [C] (ACTION)
B2 an action, movement, or sound that gives information, a message, a warning, or an order:
» When she gave (them) the signal, they all cheered.» [+ that] The firework was a signal that the festival had started.» [+ to infinitive] The police officer gave us a signal to stop.» The signal for a race to start is often the firing of a gun.Thesaurus+: ↑Signs, signals and symbols , ↑Specific signs and symbolsF0 US FOR INDICATOR(Cf. ↑indicator) (SIGNAL)
Thesaurus+: ↑The exterior of vehiclesWord Builder:–Nouns: sign, signal, signatory, signature, signing–Verbs: sign, signal• • •
Extra Examples:» At a prearranged signal, everyone started moving forwards.» I usually set my watch by the time signal on the radio.» At the given signal, the group rushed forward to the barrier.» I've been trying to call him all evening, but I keep getting the engaged signal.» A whistle is the signal for the children to line up ready to go into the classroom.noun [C] (EQUIPMENT)
► F0 equipment, especially on the side of a railway or road, often with lights, that tells drivers to stop, continue, or go more slowly: » a railway signal» a traffic signal» a road signalSee picture: a railway signal 
Thesaurus+: ↑Railways and railway linesThesaurus+: ↑Lights, signs and markings on roads
noun [C] (SHOWING)
► F0 something that shows that something else exists or is likely to happen: » The poor result is a clear signal of his deteriorating confidence.» The changing colour of the leaves on the trees is a signal that it will soon be autumn.Thesaurus+: ↑Signs, signals and symbols , ↑Specific signs and symbolsnoun [C] (WAVE)
► B2 a series of electrical or radio waves that are sent to a radio or television in order to produce a sound, picture, or messageThesaurus+: ↑Communications technology - general words• • •
Extra Examples:» The picture quality is bad because the TV signal isn't powerful enough.» The equipment sent out a regular high-pitched signal.» There is some interference on the signal - do not adjust your set.verb [I or T] (-ll- or US USUALLY -l-) (ACTION) ↑Verb Endings for signal
► C2 to make a movement, sound, flash, etc. that gives information or tells people what to do: » Flashing lights on a parked car usually signal a warning (to other motorists).» He signalled left, and turned the lorry slowly.» He was signalling (= giving a signal) with a red flag.» She signalled for help.» [+ that] She signalled to the cars behind that they were going the wrong way.» [+ obj + to infinitive ] The children's mother signalled them to be quiet.» [+ to infinitive] The children's mother signalled to/for them to be quiet.Thesaurus+: ↑Communicating and keeping in touchWord Builder:–Nouns: sign, signal, signatory, signature, signing–Verbs: sign, signal• • •
Extra Examples:» She signalled to them to sit down.» The ship signalled for help.» A flashing light signalled that there was danger ahead.» I signalled left and turned into the driveway.verb [T] (-ll- or US USUALLY -l-) (SHOW) ↑Verb Endings for signal
► F0 to show that you intend or are ready to do something: » [+ that] The union has signalled that the workers will strike.» The union has signalled the workers' intention to strike.» The death of Chairman Mao signalled (= marked) the end of an era in Chinese history.Thesaurus+: ↑Signs, signals and symbols , ↑Specific signs and symbols