Dictionary.net

Agents that promote and/or ease defecation by accelerating the passage of feces through the large intestine, by influencing the consistency and amount of stool, and by facilitating the elimination of feces from the rectum. The terms laxative and cathartic reflect the typical intensity and latency of effect. A cathartic usually produces prompt fluid evacuation, while a laxative usually produces a soft formed stool over a protracted period; the same drug may act as a laxative or a cathartic depending on the dose administered or individual patient sensitivity. (From AMA Drug Evaluations Annual, 1994, p941)