Source : Webster's Revised Unabridged Dictionary (1913)

Nocturn \Noc"turn\, n. [F. nocturne, fr. L. nocturnus. See
   {Nocturnal}, and cf. {Nocturne}.]
   1. An office of devotion, or act of religious service, by
      night.

   2. One of the portions into which the Psalter was divided,
      each consisting of nine psalms, designed to be used at a
      night service. --Hook.