The Collaborative International Dictionary of English v.0.48:

Whitewash \White"wash`\, n.
   [1913 Webster]
   1. Any wash or liquid composition for whitening something, as
      a wash for making the skin fair. --Addison.
      [1913 Webster]

   2. A composition of line and water, or of whiting size, and
      water, or the like, used for whitening walls, ceilings,
      etc.; milk of lime.
      [1913 Webster]

   3. a glossing over or cover up (of crimes or misfeasance).
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Whitewash \White"wash`\, v. t. [imp. & p. p. Whitewashed; p.
   pr. & vb. n. Whitewashing.]
   [1913 Webster]
   1. To apply a white liquid composition to; to whiten with
      whitewash.
      [1913 Webster]

   2. To make white; to give a fair external appearance to; to
      clear from imputations or disgrace; hence, to clear (a
      bankrupt) from obligation to pay debts.
      [1913 Webster]

   3. In various games, to defeat (an opponent) so that he fails
      to score, or to reach a certain point in the game; to
      skunk. [Colloq., U. S.]
      [Webster 1913 Suppl.]

   4. to gloss over or cover up (crimes or misfeasance).
      [PJC]

WordNet (r) 3.0 (2006):

whitewash
    n 1: a defeat in which the losing person or team fails to score
    2: wash consisting of lime and size in water; used for whitening
       walls and other surfaces
    3: a specious or deceptive clearing that attempts to gloss over
       failings and defects
    v 1: cover up a misdemeanor, fault, or error; "Let's not
         whitewash the crimes of Stalin"; "She tried to gloss over
         her mistakes" [syn: whitewash, gloss over, sleek
         over, hush up]
    2: cover with whitewash; "whitewash walls"
    3: exonerate by means of a perfunctory investigation or through
       biased presentation of data

Moby Thesaurus II by Grady Ward, 1.0:

199 Moby Thesaurus words for "whitewash":
   absolve, acquit, allow for, allowance, amnesty, apply paint,
   becloud, bedaub, bedizen, befog, begild, belie, besmear, blank,
   blanket, blind, brush on paint, bulldoze, calcimine, camouflage,
   chalk, clear, cloak, clobber, clobbering, cloud, coat, color,
   complexion, conceal, cover, cover up, cream, crushing defeat,
   curtain, dab, daub, decisive defeat, decontaminate,
   decontamination, deep-dye, defeat utterly, destigmatize, diminish,
   dip, discharge, disguise, dismiss, dispense from, dissemble,
   distemper, distort, distract attention from, double-dye, dress up,
   dye, ease, eclipse, embellish, emblazon, embroider, enamel, engild,
   ensconce, enshroud, envelop, exculpate, excuse, exempt,
   exempt from, exonerate, extenuate, extenuating circumstances,
   extenuation, extenuative, face, falsify, fast-dye, forgive, free,
   fresco, fudge, garble, gild, gilding, give absolution, glaze,
   gloss, gloss over, grain, grant amnesty to, grant immunity,
   grant remission, hide, hue, ignore, illuminate, imbue, ingrain,
   japan, justify, keep under cover, lacquer, lay on color, lessen,
   let go, let off, make allowance for, mask, mince, miscite,
   miscolor, misquote, misreport, misrepresent, misstate, mitigate,
   mitigation, no contest, nonpros, obfuscate, obscure, occult,
   overbear, overstate, overwhelm, overwhelming defeat, paint,
   palliate, palliation, palliative, pardon, parget, paste, pasting,
   pervert, pigment, pipe clay, pipe-clay, prime, purge,
   qualification, quash the charge, release, remit, schmear, screen,
   set free, shade, shadow, shellac, shellacking, shrive, shroud,
   shut out, skunk, slant, slop on paint, slur over, smashing defeat,
   smear, smearing, snow under, soft-pedal, soften, softening, stain,
   steamroller, stipple, strain, sugarcoat, tinct, tincture, tinge,
   tint, titivate, tone, total defeat, trick out, twist, undercoat,
   understate, utter defeat, varnish, veil, veneer, vindicate, warp,
   wash, whelm, white, whiten, whitening, whitewashing, whiting,
   whomp, whop, whopping, withdraw the charge