The Collaborative International Dictionary of English v.0.48:

Mask \Mask\, v. t. [imp. & p. p. Masked; p. pr. & vb. n.
   Masking.]
   1. To cover, as the face, by way of concealment or defense
      against injury; to conceal with a mask or visor.
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            They must all be masked and vizarded. --Shak.
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   2. To disguise; to cover; to hide.
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            Masking the business from the common eye. --Shak.
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   3. (Mil.)
      (a) To conceal; also, to intervene in the line of.
      (b) To cover or keep in check; as, to mask a body of
          troops or a fortress by a superior force, while some
          hostile evolution is being carried out.
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The Collaborative International Dictionary of English v.0.48:

Masked \Masked\, a.
   1. Wearing a mask or masks; characterized by masks;
      concealed; hidden.
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   2. (Bot.) Same as Personate.
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   3. (Zool.) Having the anterior part of the head differing
      decidedly in color from the rest of the plumage; -- said
      of birds.
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   Masked ball, a ball in which the dancers wear masks.

   Masked battery (Mil.), a battery so placed as not to be
      seen by an enemy until it opens fire. --H. L. Scott.

   Masked crab (Zool.), a European crab (Corystes
      cassivelaunus) with markings on the carapace somewhat
      resembling a human face.

   Masked pig (Zool.), a Japanese domestic hog (Sus
      pliciceps). Its face is deeply furrowed.
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WordNet (r) 3.0 (2006):

masked
    adj 1: having its true character concealed with the intent of
           misleading; "hidden agenda"; "masked threat" [syn:
           cloaked, disguised, masked]
    2: having markings suggestive of a mask; "the masked face of a
       raccoon"

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "masked":
   armored, camouflaged, cased, ceiled, cloaked, clouded, coated,
   coped, covered, covert, cowled, curtained, disguised, eclipsed,
   encapsulated, encapsuled, encased, enveloped, enwrapped, filmed,
   floored, hooded, housed, in disguise, incog, incognito, loricate,
   loricated, mantled, masquerading, muffled, obscured, occulted,
   packaged, paved, roofed-in, screened, scummed, sheathed, shelled,
   shielded, shrouded, swathed, tented, under cover, veiled, walled,
   walled-in, wrapped