c.1400, from Anglo-French and Old French pomis (13c.), from Late Latin pomicem (nominative pomex, genitive pumicis), from Oscan *poimex or some other dialectal variant of Latin pumex "pumice," from PIE *(s)poi-mo-, a root with connotations of "foam, froth" (see foam (n.)). Old English had pumic-stan. As a verb, early 15c., from the noun.
pumice pum·ice (pŭm'ĭs)
A light, porous, glassy lava, used as an abrasive.