Lewis & Short

brontĕa, ae, f. [βροντή], the thunderstone, a precious stone, Plin. 37, 10, 55, § 150.
Also called brontia, Isid. Orig. 16, 15, 24 (MSS. bronia).

brontia, v. brontea. ‡† Bronton, ontis, adj., = Βροντῶν (the thunderer), an epithet of Jupiter, Inscr. Grut. 34, 5; 17, 12; Inscr. Orell. 1272.