Source : Webster's Revised Unabridged Dictionary (1913)

Rigor \Rig"or\, n. [OE. rigour, OF. rigour, F. rigueur, from L.
   rigor, fr. rigere to be stiff. See {Rigid}.] [Written also
   {rigour}.]
   1. The becoming stiff or rigid; the state of being rigid;
      rigidity; stiffness; hardness.

            The rest his look Bound with Gorgonian rigor not to
            move.                                 --Milton.

   2. (Med.) See 1st {Rigor}, 2.

   3. Severity of climate or season; inclemency; as, the rigor
      of the storm; the rigors of winter.

   4. Stiffness of opinion or temper; rugged sternness;
      hardness; relentless severity; hard-heartedness; cruelty.

            All his rigor is turned to grief and pity. --Denham.

            If I shall be condemn'd Upon surmises, . . . I tell
            you 'T is rigor and not law.          --Shak.

   5. Exactness without allowance, deviation, or indulgence;
      strictness; as, the rigor of criticism; to execute a law
      with rigor; to enforce moral duties with rigor; -- opposed
      to {lenity}.

   6. Severity of life; austerity; voluntary submission to pain,
      abstinence, or mortification.

            The prince lived in this convent with all the rigor
            and austerity of a capuchin.          --Addison.

   7. Violence; force; fury. [Obs.]

            Whose raging rigor neither steel nor brass could
            stay.                                 --Spenser.

   Syn: Stiffness; rigidness; inflexibility; severity;
        austerity; sternness; harshness; strictness; exactness.

Source : WordNet®

rigour
     n 1: the quality of being logically valid [syn: {cogency}, {validity},
           {rigor}]
     2: something hard to endure; "the asperity of northern winters"
        [syn: {asperity}, {grimness}, {hardship}, {rigor}, {severity},
         {rigorousness}]
     3: excessive sternness; "severity of character"; "the harshness
        of his punishment was inhuman"; "the rigors of boot camp"
        [syn: {severity}, {harshness}, {rigor}, {inclemency}, {hardness},
         {stiffness}]