1. A covering worn on the face to conceal one's identity, as:a. 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.
b. A grotesque or comical representation of a face, worn especially to frighten or amuse, as at Halloween.
c. A facial covering worn for ritual.
d. A figure of a head worn by actors in Greek and Roman drama to identify a character or trait and to amplify the voice.

2. a. A protective covering for the face or head.
b. A gas mask.
c. A usually rubber frame forming a watertight seal around the eyes and nose and containing a transparent covering for use in seeing underwater.
d. A covering for the nose and mouth that is used for inhaling oxygen or an anesthetic.
e. A covering worn over the nose and mouth, as by a surgeon or dentist, to prevent infection.

3. a. A mold of a person's face, often made after death.
b. An often grotesque representation of a head and face, used for ornamentation.

4. The face or facial markings of certain animals, such as foxes or dogs.
5. A face having a blank, fixed, or enigmatic expression.
6. Something, often a trait, that disguises or conceals: "If ever I saw misery under a mask, it was on her face" (Erskine Childers).
7. A natural or artificial feature of terrain that conceals and protects military forces or installations.
8. a. An opaque border or pattern placed between a source of light and a photosensitive surface to prevent exposure of specified portions of the surface.
b. The translucent border framing a television picture tube and screen.

9. Computer Science A pattern of characters, bits, or bytes used to control the elimination or retention of another pattern of characters, bits, or bytes.
10. A cosmetic preparation that is applied to the face and allowed to dry before being removed, used especially for cleansing and tightening the skin.
11. Variant of masque.
12. A person wearing a mask.
v. masked, mask·ing, masks
v.tr.1. To cover with a decorative or protective mask.
2. To make indistinct or blurred to the senses: spices that mask the strong flavor of the meat.
3. To cover in order to conceal, protect, or disguise. See Synonyms at disguise.
4. To block the view of: Undergrowth masked the entrance to the cave.
5. To cover (a part of a photographic film) by the application of an opaque border.
6. Chemistry To prevent (an atom or a group of atoms) from taking part in a normal reaction.

v.intr.1. To put on a mask, especially for a masquerade ball.
2. To conceal one's real personality, character, or intentions.