Source : Webster's Revised Unabridged Dictionary (1913)

Cathartic \Ca*thar"tic\, Catharical \Ca*thar"ic*al\, a. [Gr. ?,
   fr. ? to cleanse, fr. ? pure; akin to F. chaste.]
   1. (Med.) Cleansing the bowels; promoting evacuations by
      stool; purgative.

   2. Of or pertaining to the purgative principle of senna, as
      cathartic acid.

Cathartic \Ca*thar"tic\, n. [Gr. ?.] (Med.)
   A medicine that promotes alvine discharges; a purge; a
   purgative of moderate activity.

   Note: The cathartics are more energetic and certain in action
         that the laxatives, which simply increase the tendency
         to alvine evacuation; and less powerful and irritaint
         that the drastic purges, which cause profuse, repeated,
         and watery evacuations. -- {Ca*thar"tic*al*ly}, adv. --
         {Ca*thar"tic*al*ness}, n.

Source : WordNet®

cathartic
     adj 1: emotionally purging [syn: {psychotherapeutic}]
     2: emotionally purging (of e.g. art) [syn: {releasing}]
     3: strongly laxative [syn: {evacuant}, {purgative}]
     n : a purging medicine; stimulates evacuation of the bowels
         [syn: {purgative}, {physic}, {aperient}]