Source : Webster's Revised Unabridged Dictionary (1913)

Rigorous \Rig"or*ous\, a. [F. rigoureux, LL. rigorosus. See
   {Rigor}.]
   1. Manifesting, exercising, or favoring rigor; allowing no
      abatement or mitigation; scrupulously accurate; exact;
      strict; severe; relentless; as, a rigorous officer of
      justice; a rigorous execution of law; a rigorous
      definition or demonstration.

            He shall be thrown down the Tarpeian Rock With
            rigorous hands.                       --Shak.

            We do not connect the scattered phenomena into their
            rigorous unity.                       --De Quincey.

   2. Severe; intense; inclement; as, a rigorous winter.

   3. Violent. [Obs.] ``Rigorous uproar.'' --Spenser.

   Syn: Rigid; inflexible; unyielding; stiff; severe; austere;
        stern; harsh; strict; exact. -- {Rig"or*ous*ly}, adv. --
        {Rig"or*ous*ness}, n.

Source : WordNet®

rigorous
     adj 1: rigidly accurate; allowing no deviation from a standard;
            "rigorous application of the law"; "a strict
            vegetarian" [syn: {strict}]
     2: demanding strict attention to rules and procedures;
        "rigorous discipline"; "tight security"; "stringent safety
        measures" [syn: {stringent}, {tight}]
     3: used of circumstances (especially weather) that cause
        suffering; "brutal weather"; "northern winters can be
        cruel"; "a cruel world"; "a harsh climate"; "a rigorous
        climate"; "unkind winters" [syn: {brutal}, {cruel}, {harsh},
         {unkind}]