Source : Webster's Revised Unabridged Dictionary (1913)

Chronometer \Chro*nom"e*ter\, n. [Gr. ? time + -meter: cf. F.
   chronom[`e]tre.]
   1. An instrument for measuring time; a timekeeper.

   2. A portable timekeeper, with a heavy compensation balance,
      and usually beating half seconds; -- intended to keep time
      with great accuracy for use an astronomical observations,
      in determining longitude, etc.

   3. (Mus.) A metronome.

   {Box chronometer}. See under {Box}.

   {Pocket chronometer}, a chronometer in the form of a large
      watch.

   {To rate a chronometer}. See {Rate}, v. t.

Source : WordNet®

chronometer
     n : an accurate clock (especially used in navigation)