The Collaborative International Dictionary of English v.0.48:

Hysteresis \Hys`te*re"sis\, n. [NL., fr. Gr. ? to be behind, to
   lag.] (Physics)
   A lagging or retardation of the effect, when the forces
   acting upon a body are changed, as if from velocity or
   internal friction; a temporary resistance to change from a
   condition previously induced, observed in magnetism,
   thermoelectricity, etc., on reversal of polarity.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hysteresis
    n 1: the lagging of an effect behind its cause; especially the
         phenomenon in which the magnetic induction of a
         ferromagnetic material lags behind the changing magnetic
         field