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.