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thunder egg

American  

noun

Geology.
  1. a globular concretion of opal, agate, or chalcedony weathered out of tuff or basalt.


Etymology

Origin of thunder egg

First recorded in 1940–45

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Steve Manford, who works at clothes shop Thunder Egg, said the arcade had had "a renaissance" in recent times.

From BBC

“It was like a thunder egg,” he says.

From Seattle Times