thunderstone

or thun·der-stone

[ thuhn-der-stohn ]
/ ˈθʌn dərˌstoʊn /

noun

any of various stones or fossils formerly thought to be fallen thunderbolts.
Archaic. a thunderbolt or flash of lightning.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for thunderstone

thunderstone
/ (ˈθʌndəˌstəʊn) /

noun

a long tapering stone, fossil, or similar object, formerly thought to be a thunderbolt
an archaic word for thunderbolt
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012