Pronunciation: (his"tu-rē'sis),[key] —n.Physics. 1. the lag in response exhibited by a body in reacting to changes in the forces, esp. magnetic forces, affecting it. Cf. magnetic hysteresis. 2. the phenomenon exhibited by a system, often a ferromagnetic or imperfectly elastic material, in which the reaction of the system to changes is dependent upon its past reactions to change.