Source : Webster's Revised Unabridged Dictionary (1913)

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.

            They must all be masked and vizarded. --Shak.

   2. To disguise; to cover; to hide.

            Masking the business from the common eye. --Shak.

   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 fortess by a superior force, while some
          hostile evolution is being carried out.

Mask \Mask\, n. [F. masque, LL. masca, mascha, mascus; cf. Sp. &
   Pg. m['a]scara, It. maschera; all fr. Ar. maskharat buffoon,
   fool, pleasantry, anything ridiculous or mirthful, fr.
   sakhira to ridicule, to laugh at. Cf. {Masque},
   {Masquerade}.]
   1. A cover, or partial cover, for the face, used for disguise
      or protection; as, a dancer's mask; a fencer's mask; a
      ball player's mask.

   2. That which disguises; a pretext or subterfuge.

   3. A festive entertainment of dancing or other diversions,
      where all wear masks; a masquerade; hence, a revel; a
      frolic; a delusive show. --Bacon.

            This thought might lead me through the world's vain
            mask.                                 --Milton.

   4. A dramatic performance, formerly in vogue, in which the
      actors wore masks and represented mythical or allegorical
      characters.

   5. (Arch.) A grotesque head or face, used to adorn keystones
      and other prominent parts, to spout water in fountains,
      and the like; -- called also {mascaron}.

   6. (Fort.)
      (a) In a permanent fortification, a redoubt which protects
          the caponiere.
      (b) A screen for a battery.

   7. (Zo["o]l.) The lower lip of the larva of a dragon fly,
      modified so as to form a prehensile organ.

   {Mask house}, a house for masquerades. [Obs.]

Mask \Mask\, v. i.
   1. To take part as a masker in a masquerade. --Cavendish.

   2. To wear a mask; to be disguised in any way. --Shak.

Mask \Mask\, n.
   1. A person wearing a mask; a masker.

            The mask that has the arm of the Indian queen. --G.
                                                  W. Cable.

   2. (Sporting) The head or face of a fox.

   {Death mask}, a cast of the face of a dead person.

Source : WordNet®

mask
     n 1: a covering to disguise or conceal the face
     2: activity that tries to conceal something; "no mask could
        conceal his ignorance"; "they moved in under a mask of
        friendship"
     3: a party of guests wearing costumes and masks [syn: {masquerade},
         {masque}]
     4: a protective covering worn over the face

mask
     v 1: hide under a false appearance; "He masked his
          disappointment" [syn: {dissemble}, {cloak}]
     2: put a mask on or cover with a mask; "Mask the children for
        Halloween" [ant: {unmask}]
     3: cover with a sauce; "mask the meat"
     4: shield from light [syn: {block out}]