1. A mineral of hydrated silica.
2. A gemstone made of this mineral, noted for its rich iridescence.
[Early Modern English, from Middle French opale, from Latin opalus, alteration of Greek opallios, probably from Sanskrit upalaḥ, stone, precious stone (often in the sandhi form opalaḥ in the names of gems such as nīlopalaḥ, sapphire : nīla-, blue + upalaḥ), possibly variant of upara-, lower, from upa, towards, under, down; see upo in the Appendix of Indo-European roots.]
opal·ine′ (ōpə-līn′, -lēn′) adj.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.