noun.
Any of several impure clayminerals consisting mostly of montmorillonite.
noun.
A porous clay formed by the decomposition of volcanic ash that swells 5 to 6 times its original volume in the presence of water.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
an absorbent aluminum silicate clay formed from volcanic ash
Word Usage
"Bentonite is a primary montmorillonite clay mined in the U.S.A., but the term bentonite is often used for other commercial montmorillonite clays as well."