Dictionary.com
definitions
  • synonyms

thunder egg

See more synonyms on Thesaurus.com
noun Geology.
  1. a globular concretion of opal, agate, or chalcedony weathered out of tuff or basalt.
Compare geode.

Origin of thunder egg

First recorded in 1940–45
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018