| opacification | 1. The process of making opaque. 2. The formation of opacities. Origin: L. Opacus, shady (05 Mar 2000) |
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| opacity | The degree to which smoke or particles emitted into the air reduce the transmission of light and obscure the view of an object in the background. (05 Dec 1998) |
| opah | <zoology> A large oceanic fish (Lampris quttatus), inhabiting the Atlantic Ocean. It is remarkable for its brilliant colours, which are red, green, and blue, with tints of purple and gold, covered with round silvery spots. Synonym: king of the herrings. Source: Websters Dictionary (01 Mar 1998) |
| opal | <chemical> A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity. The precious opal presents a peculiar play of colours of delicate tints, and is highly esteemed as a gem. One kind, with a varied play of colour in a reddish ground, is called the harlequin opal. The fire opal has colours like the red and yellow of flame. Common opal has a milky appearance. Menilite is a brown impure variety, occurring in concretions at Menilmontant, near Paris. Other varieties are cacholong, girasol, hyalite, and geyserite. Origin: L. Opalus: cf. Gr, Skr. Upala a rock, stone, precious stone: cf. F. Opale. Source: Websters Dictionary (01 Mar 1998) |
| opal codon | <molecular biology> The codon UGA, one of the three that causes termination of protein synthesis. (18 Nov 1997) |
| opal mutation | <molecular biology> Mutation that changes any codon to the termination codon UGA. (18 Nov 1997) |
| opal suppressor | <molecular biology> A gene that codes for an altered tRNA so that its anticodon can recognise the opal codon and thus allows the continuation of protein synthesis. A suppressor of an opal mutation is a tRNA that is charged with the amino acid corresponding to the original codon or a neutral substitute. Some eukaryote cells normally synthesise opal suppressor tRNAs. The function of these is not clear and they usually do not prevent normal termination of protein synthesis at an opal codon. (18 Nov 1997) |
| opalescence | <chemical> A reflection of a milky or pearly light from the interior of a mineral, as in the moonstone; the state or quality of being opalescent. Source: Websters Dictionary (01 Mar 1998) |
| opalescent | Showing a milky iridescence, like an opal. (18 Nov 1997) |
| opalescent dentin | Dentin usually associated with dentinogenesis imperfecta. It gives an unusual opalescent or translucent appearance to the teeth. Synonym: hereditary opalescent dentin. (05 Mar 2000) |
| Opalina | <protozoa> A genus of parasitic protozoans found in the guts of frogs and toads. They look superficially like ciliates, but are classified in a separate group as they have a number of similar nuclei. (18 Nov 1997) |
| opaline patch | A mucous patch of silver-gray appearance. (05 Mar 2000) |
| Opalski cell | A characteristically altered glial cell in the basal ganglia and thalamus in hepatocerebral degeneration and Wilson's disease. (05 Mar 2000) |
| Opalski, Adam | <person> Polish physician, 1897-1963. See: Opalski cell. (05 Mar 2000) |
| opaque | Impervious to light; not translucent or only slightly so. Compare: radiopaque. Origin: Fr. Fr. L. Opacus, shady (05 Mar 2000) |