b: a powder of alumina, silica, lime, iron oxide, and magnesium oxide burned together in a kiln and finely pulverized and used as an ingredient of mortar and concrete; also: any mixture used for a similar purpose
: a binding element or agency: as
a: a substance to make objects adhere to each other
b: something serving to unite firmly <justice is the cement that holds a political community together — R. M. Hutchins>
: a plastic composition made especially of zinc or silica for filling dental cavities
Agent that binds concrete and mortar. Cements are finely ground powders that, when mixed with water, set to a hard mass. The cement of 2,000 years ago was a mixture of ash and lime. Volcanic ash mined near the city of Puteoli (now Pozzuoli), near Naples, was particularly rich in essential aluminosilicate minerals, giving rise to the pozzolana cement of the Roman era. See alsoportland cement.