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