• enPR: sĭgʹnəl, IPA: /ˈsɪɡnəl/

signal (plural signals)

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.
   • 1667, John Milton, “Book V”, in Paradise Lost. A Poem Written in Ten Books, London: Printed [by Samuel Simmons], and are to be sold by Peter Parker […] [a]nd by Robert Boulter […] [a]nd Matthias Walker, […], OCLC 228722708 ↗; republished as Paradise Lost in Ten Books: The Text Exactly Reproduced from the First Edition of 1667: […], London: Basil Montagu Pickering […], 1873, OCLC 230729554 ↗:

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

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.

   He whistled to signal that we should stop.
   

7. A token; an indication; a foreshadowing; a sign.
   • c. 1593, William Shakespeare, “The Tragedy of Richard the Third: […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies: Published According to the True Originall Copies (First Folio), London: Printed by Isaac Iaggard, and Ed[ward] Blount, published 1623, OCLC 606515358 ↗, [Act V, scene iii]:

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

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

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

• (useful information) noise

• French: signal
• German: Signal
• Italian: segnale
• Portuguese: sinal
• Russian: сигна́л
• Spanish: señal

• French: signal
• German: Signal
• Italian: segnale
• Portuguese: sinal
• Spanish: señal

• Italian: segnale, campo
• Portuguese: sinal
• Spanish: señal

• French: signal

signal (signals, present participle signalling; past and past participle signalled)

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

   I signalled my acquiescence with a nod.

2. (transitive) To communicate with (a person or system) by a signal.

   Seeing the flames, he ran to the control room and signalled headquarters.

• French: signaler
• German: signalisieren
• Italian: segnalare, indicare
• Russian: сигнализи́ровать
• Spanish: señalar

signal (not comparable)

1. Standing above others in rank, importance, or achievement.

   a signal exploit; a signal service; a signal act of benevolence

   • 1671, John Milton, “Samson Agonistes, […]”, in Paradise Regain’d. A Poem. In IV Books. To which is Added, Samson Agonistes, London: Printed by J. M[acock] for John Starkey […], OCLC 228732398 ↗, [https://archive.org/stream/paradiseregaindp00milt_0#page/{page}/mode/1up page 27]:

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

• eminent, noteworthy, significant; see also Thesaurus:important or Thesaurus:notable

• signature (adjective)