any substance used for making bodies adhere to each other, as mortar, glue, etc.-a kind of calcined limestone, or a calcined mixture of clay and lime, for making mortar which will harden under water.-the powder used in cementation. see cementation, n., 2.-bond of union; that which unites firmly, as persons in friendship, or men in society.-the layer of bone investing the root and neck of a tooth; -- called also cementum.-to unite or cause to adhere by means of a cement.-to unite firmly or closely.-to overlay or coat with cement; as, to cement a cellar bottom.-to become cemented or firmly united; to cohere.