The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Christmas tree
    n 1: Australian tree or shrub with red flowers; often used in
         Christmas decoration [syn: Christmas bush, Christmas
         tree, Ceratopetalum gummiferum]
    2: a terrestrial evergreen shrub or small tree of western
       Australia having brilliant yellow-orange flowers; parasitic
       on roots of grasses [syn: flame tree, fire tree,
       Christmas tree, Nuytsia floribunda]
    3: tall timber tree of central and southern Europe having a
       regular crown and grey bark [syn: European silver fir,
       Christmas tree, Abies alba]
    4: medium to tall fir of western North America having a conic
       crown and branches in tiers; leaves smell of orange when
       crushed [syn: amabilis fir, white fir, Pacific silver
       fir, red silver fir, Christmas tree, Abies amabilis]
    5: an ornamented evergreen used as a Christmas decoration

The Jargon File (version 4.4.7, 29 Dec 2003):

Christmas tree
 n.

    A kind of RS-232 line tester or breakout box featuring rows of blinking red
    and green LEDs suggestive of Christmas lights.


The Free On-line Dictionary of Computing (30 December 2018):

Christmas tree

    A kind of EIA-232 line tester or
   breakout box featuring rows of blinking red and green LEDs
   suggestive of Christmas lights.

   [Jargon File]

   (2006-09-20)