Learner's definition of PUMICE
[noncount]
: a gray stone that comes from volcanoes, is full of small holes, has a very light weight, and is used especially for smoothing and polishing things or for softening the skin浮石,浮岩(一种火山灰岩石,尤用于抛光物体或使皮肤光滑) — called also pumice stone