Source : Webster's Revised Unabridged Dictionary (1913)

Carol \Car"ol\, v. t. [imp. & p. p. {Caroled}, or {Carolled}; p.
   pr. & vb. n. {Caroling}, or {Carolling}.]
   1. To praise or celebrate in song.

            The Shepherds at their festivals Carol her goodness.
                                                  --Milton.

   2. To sing, especially with joyful notes.

            Hovering swans . . . carol sounds harmonious.
                                                  --Prior.

Caroling \Car"ol*ing\, n.
   A song of joy or devotion; a singing, as of carols.
   --Coleridge.

         Such heavenly notes and carolings.       --Spenser.

Source : WordNet®

caroling
     n : singing joyful religious songs (especially at Christmas)