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)


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  • Stayed about 3 days there in an underground hotel. Certainly a novel experience.

    July 11, 2008

  • I've been there! It was really cool! Well... actually quite hot. But cool!

    July 11, 2008

  • I'd like to go to Coober Pedy and go down one of the opal mines. Someday.

    July 11, 2008

  • Just as well you like it then :-) I did a bit of opal fossicking around Yowah. Fun. I'm easily impressed by shiny things.

    July 11, 2008

  • Love this word ;D 'tis my middle name as well

    July 11, 2008

  • a town in Wyoming, USA

    February 26, 2008

  • Opal. The word itself was like a charm. You could stroke a word like opal. You could taste it. You could swallow it whole, raw and silky, like an oyster, and then Oyster could reel you in.
    --Janette Turner Hospital, 1996, Oyster

    November 11, 2007