Merriam-Webster Collegiate Dictionary - mask

 I. noun  Etymology: Middle French masque, from Old Italian maschera  Date: 1534  1.  a.  (1) a cover or partial cover for the face used for disguise  (2) a person wearing a ~ ; ~er  b.  (1) a figure of a head worn on the stage in antiquity to identify the character and project the voice  (2) a grotesque false face worn at carnivals or in rituals  c. an often grotesque carved head or face used as an ornament (as on a keystone)  d. a sculptured face or a copy of a face made by means of a mold  2.  a. something that serves to conceal or disguise ; pretense, cloak aware of the ~s, facades and defenses people erect to protect themselves — Kenneth Keniston  b. something that conceals from view  c. a translucent or opaque screen to cover part of the sensitive surface in taking or printing a photograph  d. a pattern of opaque material used to shield selected areas of a surface (as of a semiconductor) in deposition or etching (as in producing an integrated circuit)  3.  a. a protective covering for the face  b. gas ~  c. a device covering the mouth and nose to facilitate inhalation  d. a comparable device to prevent exhalation of infective material  e. a cosmetic preparation for the skin of the face that produces a tightening effect as it dries  4.  a. the head or face of an animal (as a fox or dog)  b. an area (as the one around the eyes) of an animal's face that is distinguished by usually darker coloring  II. verb  Date: circa 1562  intransitive verb  1. to take part in a masquerade  2.  a. to assume a ~  b. to disguise one's true character or intentions  transitive verb  1. to provide or conceal with a ~: as  a. to conceal from view ~ a gun battery  b. to make indistinct or imperceptible ~s undesirable flavors  c. to cover up ~ed his real purpose  2. to cover for protection  3. to modify the size or shape of (as a photograph) by means of an opaque border  Synonyms: see disguise  • ~like adjective