Source : Webster's Revised Unabridged Dictionary (1913)

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.]