Source : Webster's Revised Unabridged Dictionary (1913)

Christmas \Christ"mas\, n. [Christ + mass.]
   An annual church festival (December 25) and in some States a
   legal holiday, in memory of the birth of Christ, often
   celebrated by a particular church service, and also by
   special gifts, greetings, and hospitality.

   {Christmas box}.
   (a) A box in which presents are deposited at Christmas.
   (b) A present or small gratuity given to young people and
       servants at Christmas; a Christmas gift.

   {Christmas carol}, a carol sung at, or suitable for,
      Christmas.

   {Christmas day}. Same as {Christmas}.

   {Christmas eve}, the evening before Christmas.

   {Christmas fern} (Bot.), an evergreen North American fern
      ({Aspidium acrostichoides}), which is much used for
      decoration in winter.

   {Christmas flower}, {Christmas rose}, the black hellebore, a
      poisonous plant of the buttercup family, which in Southern
      Europe often produces beautiful roselike flowers
      midwinter.

   {Christmas tree}, a small evergreen tree, set up indoors, to
      be decorated with bonbons, presents, etc., and illuminated
      on Christmas eve.

Source : WordNet®

Christmas
     n 1: period extending from Dec. 24 to Jan. 6 [syn: {Christmastide},
           {Christmastime}, {Yule}, {Yuletide}, {Noel}]
     2: a Christian holiday celebrating the birth of Christ; a
        quarter day in England, Wales, and Ireland [syn: {Christmas
        Day}, {Xmas}, {Dec 25}]