sima definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
Geol. the heavy igneous rock material of the earth's inner crust, forming a continuous shell and underlying the sial and also the ocean floors
Origin: German ; from si(licium), silicium plush ma(gnesium), magnesium
sima definition by American Heritage Dictionary
The lower layer of the earth's outer crust that underlies the sial and is rich in silica, iron, and magnesium.
Origin: si(lica) + ma(gnesium).