| mask | 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. "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. 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. In a permanent fortification, a redoubt which protects the caponiere. A screen for a battery. 7. <zoology> The lower lip of the larva of a dragon fly, modified so as to form a prehensile organ. Mask house, a house for masquerades. Origin: F. Masque, LL. Masca, mascha, mascus; cf. Sp. & Pg. Mascara, It. Maschera; all fr. Ar. Maskharat buffoon, fool, pleasantry, anything ridiculous or mirthful, fr. Sakhira to ridicule, to laugh at. Cf. Masque, Masquerade. Source: Websters Dictionary (01 Mar 1998) |
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| mask of pregnancy | <medicine> A dark discolouration of the skin, usually local; as, Addison's melasma, or Addison's disease. Melasmic. Origin: NL, fr. Gr. Black spot. Source: Websters Dictionary (01 Mar 1998) |
| mask shell | <zoology> Any spiral marine shell of the genus Persona, having a curiously twisted aperture. Source: Websters Dictionary (01 Mar 1998) |
| masked | 1. Wearing a mask or masks; characterised by masks; cincealed; hidden. 2. <botany> Same as Personate. 3. <ornithology> Having the anterior part of the head differing decidedly in colour from the rest of the plumage; said of birds. Masked ball, a ball in which the dancers wear masks. Masked battery, a battery so placed as not to be seen by an enemy until it opens fire. 4. <zoology> Masked crab, a Japanese domestic hog (Sus pliciceps). Its face is deeply furrowed. Source: Websters Dictionary (01 Mar 1998) |
| masked epilepsy | A form of epilepsy characterised by a paroxysmal disturbance, such as headache or vomiting, associated with an epileptic electroencephalographic pattern. (05 Mar 2000) |
| masked gout | latent gout |
| masked hyperthyroidism | Hyperthyroidism occurring without the usual manifestations, especially lack of hyperactivity and eye findings, often with hypoactivity, even somnolence. Manifestation can be limited to heart failure. (05 Mar 2000) |
| masked messenger RNA | <molecular biology> Long lived and stable mRNA found originally in the oocytes of echinoderms and constituting a store of maternal information for protein synthesis that is unmasked (derepressed) during the early stages of morphogenesis. In these early stages the rate of cell division is so rapid that transcription from the embryonic genome cannot occur. Undoubtedly not restricted to oocytes and the term can be applied to any mRNA which is present in inactive form. (18 Nov 1997) |
| masked virus | A virus ordinarily occurring in the host in a noninfective state, but which may be activated and demonstrated by special procedures such as blind passage in experimental animals. (05 Mar 2000) |
| masking | 1. The use of noise of any kind to interfere with the audibility of another sound. For any given intensity, low pitched tones have a greater masking effect than those of a high pitch. 2. In audiology, the use of a noise applied to one ear while testing the hearing acuity of the other ear. 3. The hiding of smaller rhythms in the brain wave record by larger and slower ones whose wave form they distort. 4. In dentistry, an opaque covering used to camouflage the metal parts of a prosthesis. 5. In radiography, superimposition of an altered positive image on the original negative to produce an enhanced copy photographically. See: subtraction. (05 Mar 2000) |
| masklike face | The expressionless or masklike facies characteristic of parkinsonism. Synonym: masklike face. (05 Mar 2000) |
| masks | Protective coverings for the face, particularly the mouth and nose, to maintain antiseptic conditions, to protect the wearer from contamination and to prevent droplets from the wearer's nose and mouth from spreading in the air. It includes surgical masks worn in the operating room and dentists' offices. It refers also to devices designed to cover the mouth and nose for administration of inhalation anaesthetics, oxygen, or other gases. (12 Dec 1998) |
| Hutchinson's mask | The sensation experienced in tabetic neurosyphilis as if the face were covered with a mask or with cobwebs. (05 Mar 2000) |
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| shadow mask | <microscopy> Also Aperture mask. In colour video monitors, a finely perforated or striped metal plate that is located between the three electron guns and the phosphor screen. The mask ensures that the electron beams carrying the R, G, and B signals land on the corresponding phosphors at every point in the picture. (05 Aug 1998) |
| nonrebreathing mask | A mask fitted with both an inhalation valve and an exhalation valve so that all exhaled gas is vented to the external atmosphere and inhaled gas comes only from a reservoir connected to the mask. (05 Mar 2000) |
| ecchymotic mask | A dusky discoloration of the head and neck occurring when the trunk has been subjected to sudden and extreme compression, as in traumatic asphyxia. (05 Mar 2000) |
| tropical mask | A bronze-coloured pigmentation, probably produced by hormone imbalance, occurring in gradually increasing areas on the face, neck, and chest in persons exposed continuously to the tropical sun; similar to chloasma of the temperate zone, but intensified because of strong sunlight. Synonym: tropical mask. (05 Mar 2000) |
| laryngeal mask | A tubular oropharyngeal airway with an inflatable rim at the distal end that when inflated creates an airtight seal immediately above the larynx. (05 Mar 2000) |
| luetic mask | A dirty brownish yellow pigmentation, blotchy in character, resembling that of chloasma, occurring on the forehead, temples, and sometimes the cheeks in patients with tertiary syphilis. (05 Mar 2000) |