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
    adj 1: completely neat and clean; "the apartment was
           immaculate"; "in her immaculate white uniform"; "a spick-
           and-span kitchen"; "their spic red-visored caps" [syn:
           immaculate, speckless, spick-and-span, spic-and-
           span, spic, spick, spotless]
    2: free from stain or blemish [syn: immaculate, undefiled]
    3: without fault or error; "faultless logic"; "speaks impeccable
       French"; "timing and technique were immaculate"; "an
       immaculate record" [syn: faultless, immaculate,
       impeccable]

Moby Thesaurus II by Grady Ward, 1.0:

125 Moby Thesaurus words for "immaculate":
   Christian, absolute, beyond all praise, blameless, bleached,
   blotless, bright, chaste, clean, cleanly, creditable, dainty,
   dapper, decent, defectless, dirt-free, erect, errorless, estimable,
   ethical, exquisite, fair, fastidious, faultless, flawless, fresh,
   full of integrity, good, guiltless, high-minded, high-principled,
   highly respectable, honest, honorable, ideal, impeccable,
   indefectible, indefective, infallible, innocent, inviolate,
   irreproachable, just, just right, kosher, law-abiding, law-loving,
   law-revering, manly, modest, moral, neat, noble, nonpolluted,
   of cleanly habits, peerless, perfect, principled, pristine, pure,
   pure in heart, purehearted, reputable, respectable, right,
   right-minded, righteous, ritually pure, sexually innocent, shiny,
   sinless, smut-free, smutless, snow-white, snowy, spick and span,
   spotless, spruce, stainless, sterling, sweet, tahar, taintless,
   tidy, true-dealing, true-devoted, true-disposing, true-souled,
   true-spirited, truehearted, tubbed, unadulterated, unbesmirched,
   unblemished, unblotted, uncontaminated, uncorrupt, uncorrupted,
   undefiled, unfaultable, unimpeachable, unmixed, unmuddied,
   unpolluted, unsmirched, unsmudged, unsoiled, unspoiled, unspotted,
   unstained, unsullied, untainted, untarnished, upright, uprighteous,
   upstanding, vestal, virginal, virtuous, well-scrubbed, well-washed,
   white, whitened, worthy, yeomanly