1. A material or a mixture of materials (without aggregate) which, when in a plastic state, possesses adhesive and cohesive properties and hardens in place. Frequently, the term is used incorrectly for concrete, e.g., a cement block for concrete block. See also portland cement.
2. A calcined combination of limestone and clay, combined with an aggregate that reacts chemically when water is added;
after this reaction occurs, the mixture hardens in place as it dries, resulting in a stonelike material. Although the ancient Romans developed a cement that could harden under water (called hydraulic cement), there was little information in modern times on how to produce such a cement until the mid-1700s when experiments in England led to the development of a cement that could set quickly, in or out of water.
Also see hydraulic cement, portland cement, Roman cement, water cement.