pumice

n. [ L. pumex, pumicis, prob. akin to spuma foam: cf. AS. pumic-stān. Cf. Pounce a powder, Spume. ] (Min.) A very light porous volcanic scoria, usually of a gray color, the pores of which are capillary and parallel, giving it a fibrous structure. It is supposed to be produced by the disengagement of watery vapor without liquid or plastic lava. It is much used, esp. in the form of powder, for smoothing and polishing. Called also pumice stone. [ 1913 Webster ]

a. (Far.) Affected with a kind of chronic laminitis in which there is a growth of soft spongy horn between the coffin bone and the hoof wall. The disease is called pumiced foot, or pumice foot. [ 1913 Webster ]

a. [ L. pumiceus. ] Of or pertaining to pumice; resembling pumice. [ 1913 Webster ]