Source : Webster's Revised Unabridged Dictionary (1913)

Pitiless \Pit"i*less\, a.
   1. Destitute of pity; hard-hearted; merciless; as, a
      pitilessmaster; pitiless elements.

   2. Exciting no pity; as, a pitiless condition. --
      {Pit"i*less*ly}, adv. -- {Pit"i*less*ness}, n.

Source : WordNet®

pitilessness
     n 1: feelings of extreme heartlessness [syn: {cruelty}, {mercilessness},
           {ruthlessness}]
     2: mercilessness characterized by a lack of pity [syn: {ruthlessness}]