Definition of opal

< opah

opalesce >

o·pal    (pl) KEY 

NOUN:

1. A mineral of hydrated silica.
2. A gemstone made of this mineral, noted for its rich iridescence.

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ETYMOLOGY:
Middle English opalus, from Latin, alteration of Greek opallios, probably from Sanskrit upala, from variant of upara-, lower, from upa, below; see upo in Indo-European roots

OTHER FORMS:
opal·ine  (p-ln, -ln) KEY (Adjective)