Source : Webster's Revised Unabridged Dictionary (1913)

Signal \Sig"nal\, n. [F., fr. LL. signale, fr. L. signum. See
   {Sign}, n.]
   1. A sign made for the purpose of giving notice to a person
      of some occurence, command, or danger; also, a sign,
      event, or watchword, which has been agreed upon as the
      occasion of concerted action.

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

   2. A token; an indication; a foreshadowing; a sign.

            The weary sun . . . Gives signal of a goodly day
            to-morrow.                            --Shak.

            There was not the least signal of the calamity to be
            seen.                                 --De Foc.

Signal \Sig"nal\, v. t. [imp. & p. p. {Signaled or Signalled};
   p. pr. & vb. n. {Signaling} or {Signalling}.]
   1. To communicate by signals; as, to signal orders.

   2. To notify by a signals; to make a signal or signals to;
      as, to signal a fleet to anchor. --M. Arnold.

Signal \Sig"nal\, a. [From signal, n.: cf. F. signal['e].]
   1. Noticeable; distinguished from what is ordinary; eminent;
      remarkable; memorable; as, a signal exploit; a signal
      service; a signal act of benevolence.

            As signal now in low, dejected state As erst in
            highest, behold him where he lies.    --Milton.

   2. Of or pertaining to signals, or the use of signals in
      conveying information; as, a signal flag or officer.

   {The signal service}, a bureau of the government (in the
      United States connected with the War Department) organized
      to collect from the whole country simultaneous raports of
      local meteorological conditions, upon comparison of which
      at the central office, predictions concerning the weather
      are telegraphed to various sections, where they are made
      known by signals publicly displayed.

   {Signal station}, the place where a signal is displayed;
      specifically, an observation office of the signal service.

   Syn: Eminent; remarkable; memorable; extraordinary; notable;
        conspicuous.

Source : WordNet®

signal
     adj : notably out of the ordinary; "the year saw one signal
           triumph for the Labour party"
     [also: {signalling}, {signalled}]

signal
     n 1: any communication that encodes a message; "signals from the
          boat suddenly stopped" [syn: {signaling}, {sign}]
     2: any incitement to action; "he awaited the signal to start";
        "the victory was a signal for wild celebration"
     3: an electric quantity (voltage or current or field strength)
        whose modulation represents coded information about the
        source from which it comes
     [also: {signalling}, {signalled}]

signal
     v 1: communicate silently and non-verbally by signals or signs;
          "He signed his disapproval with a dismissive hand
          gesture"; "The diner signaled the waiters to bring the
          menu" [syn: {sign}, {signalize}, {signalise}]
     2: be a signal for or a symptom of; "These symptoms indicate a
        serious illness"; "Her behavior points to a severe
        neurosis"; "The economic indicators signal that the euro
        is undervalued" [syn: {bespeak}, {betoken}, {indicate}, {point}]
     [also: {signalling}, {signalled}]

Source : Free On-Line Dictionary of Computing

SIGNAL
     
         A synchronous language by Le Guernic et al of
        {INRIA}.
     
        ["SIGNAL - A Data Flow-Oriented Language for Signal
        Processing," P. le Guernic, IEEE Trans Acoustics Speech &
        Signal Proc, ASSP-34(2):362-1986-04-374].
     
        (1996-12-10)

signal
     
         A predefined message sent between two
        {Unix} {processes} or from the {kernel} to a process.  Signals
        communicate the occurrence of unexpected external events such
        as the forced termination of a process by the user.  Each
        signal has a unique number associated with it and each process
        has a signal handler set for each signal.  Signals can be sent
        using the {kill} {system call}.
     
        (1996-12-10)