pozzuolana

from The Collaborative International Dictionary of English v.0.48

Pozzuolana \Poz`zu*o*la"na\, Pozzolana \Poz`zo*la"*na\, n. [It.]
   Volcanic ashes from Pozzuoli, in Italy, used in the
   manufacture of a kind of mortar which hardens under water.
   [1913 Webster]