\rә-▐ji-dә-tē\ n (1624) The ability of a structure to resist deformation under load. It is a function of both the material’s modulus of elasticity and, often more critically, of the geometry of the structure. In a loaded beam, whatever the load distribution or type of beam supports, the maximum deflection is inversely proportional to the product, EċI, of the material’s elastic modulus and the moment of inertia of the beam’s cross-section about its neutral axis. See also Section Modulus. The term rigidity is often applied loosely to materials themselves without reference to a particular structure when what the speaker actually has in mind is the elastic modulus.