ˈōpəl noun
( -s )
Usage: often attributive
Etymology: Latin opalus, from Sanskrit upala stone, jewel, upper millstone; perhaps akin to Sanskrit upari over — more at over
1. : a mineral SiO 2 . n H 2 O that is a hydrated amorphous silica softer and less dense than quartz and typically with definite and often marked iridescent play of colors — see black opal , harlequin opal
2.
a. : opal glass
b. : opaline