Any substance that accelerates defecation. Compare with laxatives, which are substances that ease defecation (usually by softening faeces). A substance can be both a laxative and a cathartic.
An agent that produces a soft formed stool, and relaxes and loosens the bowels, typically used over a protracted period, to relieve constipation. Compare with cathartic, which is a substance that accelerates defecation. A substances can be both a laxative and a cathartic.