Definition from Wiktionary, the free dictionary
- a clear-to-white liquid secreted by sea hares (genus Aplysia) that becomes viscous upon contact with water
- The attack on a sea hare by a spiny lobster causes release of the whitish opaline, followed the co-release of both opaline and ink.
- (mineralogy) any of several minerals resembling opal, including a variety of yellow chalcedony
- opal glass