signal

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.

   “All obeyed / The wonted signal and superior voice / Of this great potentate.”

   “Banner-Repeater signals tend to be provided in locations where drivers receive insufficient warning of the main signal, thereby effectively increasing the sighting distance for the main signal.”

4. An on-off light, semaphore, or other device used to give an indication to another person.
5. An on-off light, semaphore, or other device used to give an indication to another person.
6. (Internet, TV, usually)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.”

7. An action, change or process done to convey information and thus reduce uncertainty.
8. A token; an indication; a foreshadowing; a sign.

   “The weary sun […] / Gives signal of a goodly day to-morrow.”

   “There was not the least signal of the calamity to be seen.”

   “Did I get it wrong all along? / You were sending signals / You sent certain signals to me”

9. Useful information, as opposed to noise.
10. (Unix)A simple interprocess communication used to notify a process or thread of an occurrence.
11. A signalling interaction between cells

verb

1. (ambitransitive)To indicate; to convey or communicate by a signal.

   “I signalled my acquiescence with a nod.”

   “He whistled to signal that we should stop.”

   “My arms wheeled frantically in the air as I tried to signal for help.”

   “In order to accommodate the new platform 4 and the reversibly signalled slow line, a deep cutting had to be cut back and held up in places with a concrete retaining wall.”

   “I signaled for our waiter and ordered two Glenlivets, the only single malt they had behind the bar.”

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. (not-comparable)Standing above others in rank, importance, or achievement.

   “a signal exploit; a signal success; a signal act of benevolence”

   “As ſignal now in low dejected ſtate, / As earſt in higheſt, behold him where he lies.”

   “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.”