signal

Etymology

From Old French segnal, seignal or Medieval Latin signāle; noun use of the neuter of Late Latin signālis, from Latin signum; verb use from 1805, as a shortened from signalize (1650s).

noun

1. A sequence of states representing an encoded message in a communication channel.
2. Any variation of a quantity or change in an entity over time that conveys information upon detection.
3. A sign made to give notice of some occurrence, command, or danger, or to indicate the start of a concerted action.
4. An on-off light, semaphore, or other device used to give an indication to another person.
5. (of a radio, TV, telephone, internet, etc.) An electromagnetic action, normally a voltage that is a function of time, that conveys the information of the radio or TV program or of communication with another party.
   My mobile phone can't get a signal in the railway station.
6. An action, change or process done to convey information and thus reduce uncertainty.
7. A token; an indication; a foreshadowing; a sign.
   There was not the least signal of the calamity to be seen. 1722, Daniel Defoe, A Journal of the Plague Year
8. Useful information, as opposed to noise.
9. (computing, Unix) A simple interprocess communication used to notify a process or thread of an occurrence.
10. (biochemistry) A signalling interaction between cells

verb

1. (transitive, intransitive) To indicate; to convey or communicate by a signal.
   I signalled my acquiescence with a nod.
   He whistled to signal that we should stop.
2. (transitive) To communicate with (a person or system) by a signal.
   Seeing the flames, he ran to the control room and signalled headquarters.

adj

1. Standing above others in rank, importance, or achievement.
   a signal exploit; a signal success; a signal act of benevolence
   But, setting this view aside, dishonorable would it be in the South were she willing to abandon to shame the memory of brave men who with signal personal disinterestedness warred in her behalf, though from motives, as we believe, so deplorably astray. 1866, Herman Melville, Battle-Pieces and Aspects of the War, Supplement