The Collaborative International Dictionary of English v.0.48:

Winter \Win"ter\, n. [AS. winter; akin to OFries. & D. winter,
   OS. & OHG. wintar, G. winter, D. & Sw. vinter, Icel. vetr,
   Goth. wintrus; of uncertain origin; cf. Old Gallic vindo-
   white (in comp.), OIr. find white. ????.]
   [1913 Webster]
   1. The season of the year in which the sun shines most
      obliquely upon any region; the coldest season of the year.
      "Of thirty winter he was old." --Chaucer.
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            And after summer evermore succeeds
            Barren winter, with his wrathful nipping cold.
                                                  --Shak.
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            Winter lingering chills the lap of May. --Goldsmith.
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   Note: North of the equator, winter is popularly taken to
         include the months of December, January, and February
         (see Season). Astronomically, it may be considered to
         begin with the winter solstice, about December 21st,
         and to end with the vernal equinox, about March 21st.
         [1913 Webster]

   2. The period of decay, old age, death, or the like.
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            Life's autumn past, I stand on winter's verge.
                                                  --Wordsworth.
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   Winter apple, an apple that keeps well in winter, or that
      does not ripen until winter.

   Winter barley, a kind of barley that is sown in autumn.

   Winter berry (Bot.), the name of several American shrubs
      (Ilex verticillata, Ilex laevigata, etc.) of the Holly
      family, having bright red berries conspicuous in winter.


   Winter bloom. (Bot.)
      (a) A plant of the genus Azalea.
      (b) A plant of the genus Hamamelis (Hamamelis
          Viginica); witch-hazel; -- so called from its flowers
          appearing late in autumn, while the leaves are
          falling.

   Winter bud (Zool.), a statoblast.

   Winter cherry (Bot.), a plant (Physalis Alkekengi) of the
      Nightshade family, which has, a red berry inclosed in the
      inflated and persistent calyx. See Alkekengi.

   Winter cough (Med.), a form of chronic bronchitis marked by
      a cough recurring each winter.

   Winter cress (Bot.), a yellow-flowered cruciferous plant
      (Barbarea vulgaris).

   Winter crop, a crop which will bear the winter, or which
      may be converted into fodder during the winter.

   Winter duck. (Zool.)
      (a) The pintail.
      (b) The old squaw.

   Winter egg (Zool.), an egg produced in the autumn by many
      invertebrates, and destined to survive the winter. Such
      eggs usually differ from the summer eggs in having a
      thicker shell, and often in being enveloped in a
      protective case. They sometimes develop in a manner
      different from that of the summer eggs.

   Winter fallow, ground that is fallowed in winter.

   Winter fat. (Bot.) Same as White sage, under White.

   Winter fever (Med.), pneumonia. [Colloq.]

   Winter flounder. (Zool.) See the Note under Flounder.

   Winter gull (Zool.), the common European gull; -- called
      also winter mew. [Prov. Eng.]

   Winter itch. (Med.) See Prarie itch, under Prairie.

   Winter lodge, or Winter lodgment. (Bot.) Same as
      Hibernaculum.

   Winter mew. (Zool.) Same as Winter gull, above. [Prov.
      Eng.]

   Winter moth (Zool.), any one of several species of
      geometrid moths which come forth in winter, as the
      European species (Cheimatobia brumata). These moths have
      rudimentary mouth organs, and eat no food in the imago
      state. The female of some of the species is wingless.

   Winter oil, oil prepared so as not to solidify in
      moderately cold weather.

   Winter pear, a kind of pear that keeps well in winter, or
      that does not ripen until winter.

   Winter quarters, the quarters of troops during the winter;
      a winter residence or station.

   Winter rye, a kind of rye that is sown in autumn.

   Winter shad (Zool.), the gizzard shad.

   Winter sheldrake (Zool.), the goosander. [Local, U. S.]

   Winter sleep (Zool.), hibernation.

   Winter snipe (Zool.), the dunlin.

   Winter solstice. (Astron.) See Solstice, 2.

   Winter teal (Zool.), the green-winged teal.

   Winter wagtail (Zool.), the gray wagtail (Motacilla
      melanope). [Prov. Eng.]

   Winter wheat, wheat sown in autumn, which lives during the
      winter, and ripens in the following summer.

   Winter wren (Zool.), a small American wren (Troglodytes
      hiemalis) closely resembling the common wren.
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WordNet (r) 3.0 (2006):

winter solstice
    n 1: December 22, when the sun is at its southernmost point
         [ant: June 21, midsummer, summer solstice]