from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A mineral of hydrated silica.
- n. A gemstone made of this mineral, noted for its rich iridescence.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity, of the chemical formula SiO2·nH2O.
- n. , (genetics), (biochemistry) A colloquial name used in molecular biology referring to a particular stop codon sequence, "UGA."
from the GNU version of the Collaborative International Dictionary of English
- n. A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.
from The Century Dictionary and Cyclopedia
- n. A mineral consisting of silica like quartz, but in a different condition, having a lower specific gravity and hardness and being without crystalline structure: it usually contains some water, mostly from 3 to 9 per cent. ; ; ; ; ; ; ;
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
Middle English opalus, from Latin, alteration of Greek opallios, probably from Sanskrit upalaḥ, from variant of upara-, lower, from upa, below.(American Heritage® Dictionary of the English Language, Fourth Edition)
In Florio’s A World of Words 1598 as opale, from French opale, from Latin opalus, from Byzantine Greek ὀπάλλιος (opallios), from Sanskrit उपल (upala, "gem”, “stone"). (Wiktionary)