The Collaborative International Dictionary of English v.0.48:

Nativity \Na*tiv"i*ty\, n.; pl. Nativies. [F. nativit['e], L.
   nativitas. See Native, and cf. Na["i]vet['e].]
   1. The coming into life or into the world; birth; also, the
      circumstances attending birth, as time, place, manner,
      etc. --Chaucer.
      [1913 Webster]

            I have served him from the hour of my nativity.
                                                  --Shak.
      [1913 Webster]

            Thou hast left . . . the land of thy nativity.
                                                  --Ruth ii. 11.
      [1913 Webster]

            These in their dark nativity the deep
            Shall yield us, pregnant with infernal flame.
                                                  --Milton.
      [1913 Webster]

   2. (Fine Arts) (capitalized) A picture representing or
      symbolizing the early infancy of Christ. The simplest form
      is the babe in a rude cradle, and the heads of an ox and
      an ass to express the stable in which he was born.
      [1913 Webster]

   3. (Astrol.) A representation of the positions of the
      heavenly bodies as the moment of one's birth, supposed to
      indicate one's future destinies; a horoscope.
      [1913 Webster]

   The Nativity, the birth or birthday of Christ; Christmas
      day.

   To cast one's nativity or To calculate one's nativity
      (Astrol.), to find out and represent the position of the
      heavenly bodies at the time of one's birth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nativity
    n 1: the event of being born; "they celebrated the birth of
         their first child" [syn: birth, nativity, nascency,
         nascence] [ant: death, decease, expiry]
    2: the theological doctrine that Jesus Christ had no human
       father; Christians believe that Jesus's birth fulfilled Old
       Testament prophecies and was attended by miracles; the
       Nativity is celebrated at Christmas [syn: Virgin Birth,
       Nativity]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "nativity":
   aboriginality, accouchement, aspect, astrodiagnosis, astrology,
   astromancy, autochthonousness, babyhood, beginnings, birth,
   birth throes, birthing, blessed event, childbearing, childbed,
   childbirth, childhood, confinement, cradle, delivery,
   freshman year, genesis, genethliac astrology, genethliacism,
   genethliacs, genethlialogy, giving birth, hatching, having a baby,
   horoscope, horoscopy, house, inception, inchoation, incipience,
   incipiency, incunabula, indigenousness, infancy, labor, mansion,
   multiparity, mundane astrology, mundane house, nascence, nascency,
   nationality, native-bornness, nativeness, nativism,
   natural astrology, origin, origination, parturition,
   planetary house, pregnancy, stargazing, the Nativity, the stork,
   travail, youth, zodiac