Source : Webster's Revised Unabridged Dictionary (1913)

Christianity \Chris*tian"i*ty\, n. [OE. cristiente, OF.
   cristient['e], F. chr['e]tient['e], fr. L. christianitas. ]
   1. The religion of Christians; the system of doctrines and
      precepts taught by Christ.

   2. Practical conformity of one's inward and outward life to
      the spirit of the Christian religion

   3. The body of Christian believers. [Obs.]

            To Walys fled the christianitee Of olde Britons.
                                                  --Chaucer.

Source : WordNet®

Christianity
     n 1: a monotheistic system of beliefs and practices based on the
          Old Testament and the teachings of Jesus as embodied in
          the New Testament and emphasizing the role of Jesus as
          savior [syn: {Christian religion}]
     2: the collective body of Christians throughout the world and
        history (found predominantly in Europe and the Americas
        and Australia); "for a thousand years the Roman Catholic
        Church was the principal church of Christendom" [syn: {Christendom}]