Source : Webster's Revised Unabridged Dictionary (1913)

Viol \Vi"ol\, n. [F. viole; cf. Pr. viola, viula, Sp., Pg., &
   It. viola, LL. vitula; of uncertain origin; perhaps from L.
   vitulari to celebrate a festival, keep holiday, be joyful,
   perhaps originally, to sacrifice a calf (vitulus; cf.
   {Veal}). Cf. {Fiddle}, {Vielle}, 2d {Viola}, {Violin}.]
   1. (Mus.) A stringed musical instrument formerly in use, of
      the same form as the violin, but larger, and having six
      strings, to be struck with a bow, and the neck furnished
      with frets for stopping the strings.

            Me softer airs befit, and softer strings Of lute, or
            viol still, more apt for mournful things. --Milton.

   Note: The name is now applied as a general term to designate
         instruments of the violin kind, as tenor viol, bass
         viol, etc.

   2. (Naut.) A large rope sometimes used in weighing anchor.
      [Written also {voyal}, and {voyal}.] --Totten.

Source : WordNet®

viol
     n : any of a family of bowed stringed instruments that preceded
         the violin family