mask

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A covering worn on the face to conceal one's identity, as.
• noun A covering, as of cloth, that has openings for the eyes, entirely or partly conceals the face, and is worn especially at a masquerade ball.
• noun A grotesque or comical representation of a face, worn especially to frighten or amuse, as at Halloween.
• noun A facial covering worn for ritual.
• noun A figure of a head worn by actors in Greek and Roman drama to identify a character or trait and to amplify the voice.
• noun A protective covering for the face or head.
• noun A gas mask.
• noun A usually rubber frame forming a watertight seal around the eyes and nose and containing a transparent covering for use in seeing underwater.
• noun A covering for the nose and mouth that is used for inhaling oxygen or an anesthetic.
• noun A covering worn over the nose and mouth, as by a surgeon or dentist, to prevent infection.
• noun A mold of a person's face, often made after death.
• noun An often grotesque representation of a head and face, used for ornamentation.
• noun An area of contrasting color on the face and usually across the eyes of an animal.
• noun The head, face, or muzzle of certain animals, such as a fox or a dog.
• noun A face having a blank, fixed, or enigmatic expression.
• noun Something, often a trait, that disguises or conceals.
• noun A natural or artificial feature of terrain that conceals and protects military forces or installations.
• noun An opaque border or pattern placed between a source of light and a photosensitive surface to prevent exposure of specified portions of the surface.
• noun The translucent border framing a television picture tube and screen.
• noun Computers A pattern of characters, bits, or bytes used to control the elimination or retention of another pattern of characters, bits, or bytes.
• noun A cosmetic preparation that is applied to the face and allowed to dry before being removed, used especially for cleansing and tightening the skin.
• noun A person wearing a mask.
• intransitive verb To cover (the face, for example) with a decorative or protective mask.
• intransitive verb To cover in order to conceal, protect, or disguise.
• intransitive verb To make indistinct or difficult to perceive.
• intransitive verb To conceal by dissembling: synonym: disguise.
• intransitive verb Chemistry To prevent (an atom or a group of atoms) from taking part in a normal reaction.
• intransitive verb To put on a mask, especially for a masquerade ball.
• intransitive verb To conceal one's real personality, emotion, or intention.

from The Century Dictionary.

• To steep; infuse.
• To be infused; yield to the process of infusion: as, the tea is masking.
• To cover the face of, wholly or in part, for concealment, disguise, or defense; conceal with a mask or vizor.
• To cover with a disguising costume of any kind, as in a masquerade.
• To disguise; conceal; screen from view by something interposed.
• Synonyms To cloak, veil, screen, shroud.
• To play a part in a masquerade; go about in masquerade.
• To put on a mask; disguise one's self in any way.
• An obsolete form of mesh.
• noun In zoology: The skin of the forehead and upper part of the face of any quadruped, taken off at about the level of the eyes.
• noun In base-ball, a protection for the face worn by the catcher. See cage, 8.
• noun A cover for the face with apertures for seeing and breathing; especially, such a cover, usually of silk or velvet, as worn at masquerades; a false face; a vizor.
• noun A festive entertainment or performance in which the participants are masked or wear a disguising costume; a body of maskers; a masquerade; a revel.
• noun A form of histrionic spectacle, much in vogue during the sixteenth and seventeenth centuries.
• noun Anything used or practised for disguise or concealment; anything interposed as a safeguard against observation, discovery, or disclosure; a screen or disguise; a subterfuge, pretext, or shift: as, a mask of brush in front of a battery; suffering under a mask of gaiety.