The Collaborative International Dictionary of English v.0.48:

Rigor \Ri"gor\, n. [L. See Rigor., below.]
   1. Rigidity; stiffness.
      [1913 Webster]

   2. (ed.) A sense of chilliness, with contraction of the skin;
      a convulsive shuddering or tremor, as in the chill
      preceding a fever.
      [1913 Webster]

   Rigor caloris[L., rigor of heat] (Physiol.), a form of
      rigor mortis induced by heat, as when the muscle of a
      mammal is heated to about 50[deg] C.

   Rigor mortis[L., rigor of death], death stiffening; the
      rigidity of the muscles that occurs at death and lasts
      till decomposition sets in. It is due to the formation of
      myosin by the coagulation of the contents of the
      individual muscle fibers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rigor mortis
    n 1: temporary stiffness of joints and muscular rigidity
         occurring after death
    2: muscular stiffening that begins 2 to 4 hours after death and
       lasts for about 4 days