1. To harden by chemical hydration. 2. A change from a plastic to a hard state. 3. The change in mortar or plaster from a plastic, workable state to a solid, rigid state. 4. The condition reached by a cement paste, mortar, or concrete when it has lost plasticity to an arbitrary degree, usually measured in terms of resistance to penetration or deformation; initial set refers to first stiffening; final set refers to attainment of significant rigidity. 5. A chisel used for cutting brick.