Entry 2 senses Webster, 1913 Thunderstone · Thun·der·stone · IPA 01 n. A thunderbolt, -- formerly believed to be a stone. 1. A thunderbolt, -- formerly believed to be a stone. “Fear no more the lightning flash, Nor the all-dreaded thunderstone.” — Shak. 2. A belemnite. See Belemnite.(Paleon.) See: Belemnite