Source : Webster's Revised Unabridged Dictionary (1913)

Tocsin \Toc"sin\, n. [F., fr. OF. toquier to touch, F. toquer
   (originally, a dialectic form of F. toucher) + seint (for
   sein) a bell, LL. signum, fr. L. signum a sign, signal. See
   {Touch}, and {Sign}.]
   An alarm bell, or the ringing of a bell for the purpose of
   alarm.

         The loud tocsin tolled their last alarm. --Campbell.

Source : WordNet®

tocsin
     n 1: the sound of an alarm (usually a bell) [syn: {alarm bell}]
     2: a bell used to sound an alarm [syn: {warning bell}]