Tōad'-stōne, n.
n. 1. (Min.) A variety of trap-rock, of a brownish-gray color; especially, a variety of trap found in Derbyshire, which is generally a dark-brown basaltic amygdaloid, composed of basalt and green earth, and containing oblong cavities filled with calcareous spar.
☞ The name is said by some to be derived from the German todt stein, meaning dead stone, that is, stone which contains no ores.
Sense 2. A kind of jewel or precious stone formerly popularly supposed to be contained in the head of a toad. See TOAD.