The Collaborative International Dictionary of English v.0.48:

Immaculate \Im*mac"u*late\, a. [L. immaculatus; pref. im- not +
   maculatus, p. p. of maculare to spot, stane, fr. macula spot.
   See Mail armor.]
   Without stain or blemish; spotless; undefiled; clear; pure.
   [1913 Webster]

         Were but my soul as pure
         From other guilt as that, Heaven did not hold
         One more immaculate.                     --Denham.
   [1913 Webster]

         Thou sheer, immaculate and silver fountain. --Shak.
   [1913 Webster]

   Immaculate conception (R. C. Ch.), the doctrine that the
      Virgin Mary was conceived without original sin. --
      Im*mac"u*late*ly, adv. -- Im*mac"u*late*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Immaculate Conception
    n 1: Roman Catholic holy day first celebrated in 1854 [syn:
         Immaculate Conception, December 8]
    2: (Christianity) the Roman Catholic dogma that God preserved
       the Virgin Mary from any stain of original sin from the
       moment she was conceived [syn: Immaculate Conception,
       Immaculate Conception of the Virgin Mary]