The Collaborative International Dictionary of English v.0.48:

Ascetic \As*cet"ic\a. [Gr. ?, fr. ? to exercise, to practice
   gymnastics.]
   Extremely rigid in self-denial and devotions; austere;
   severe.
   [1913 Webster]

         The stern ascetic rigor of the Temple discipline. --Sir
                                                  W. Scott.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ascetic \As*cet"ic\, n.
   In the early church, one who devoted himself to a solitary
   and contemplative life, characterized by devotion, extreme
   self-denial, and self-mortification; a hermit; a recluse;
   hence, one who practices extreme rigor and self-denial in
   religious things.
   [1913 Webster]

         I am far from commending those ascetics that take up
         their quarters in deserts.               --Norris.
   [1913 Webster]

   Ascetic theology, the science which treats of the practice
      of the theological and moral virtues, and the counsels of
      perfection. --Am. Cyc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ascetic
    adj 1: pertaining to or characteristic of an ascetic or the
           practice of rigorous self-discipline; "ascetic practices"
           [syn: ascetic, ascetical]
    2: practicing great self-denial; "Be systematically
       ascetic...do...something for no other reason than that you
       would rather not do it"- William James; "a desert nomad's
       austere life"; "a spartan diet"; "a spartan existence" [syn:
       ascetic, ascetical, austere, spartan]
    n 1: someone who practices self denial as a spiritual discipline
         [syn: abstainer, ascetic]