The Collaborative International Dictionary of English v.0.48:

Purgative \Pur"ga*tive\, a. [L. purgativus: cf. F. purgatif.]
   Having the power or quality of purging; cathartic. -- n.
   (Med.) A purging medicine; a cathartic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

purgative
    adj 1: strongly laxative [syn: cathartic, evacuant,
           purgative]
    n 1: a purging medicine; stimulates evacuation of the bowels
         [syn: purgative, cathartic, physic, aperient]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "purgative":
   abstergent, alleviating, alleviative, analgesic, anesthetic,
   anodyne, aperient, apologetic, ascetic, assuasive, atoning, balmy,
   balsamic, benumbing, carminative, cathartic, cleaner, cleaning,
   cleaning agent, cleaning solvent, cleanser, cleansing,
   cleansing cream, cold cream, compensational, compensatory, cream,
   deadening, demulcent, dentifrice, depurant, depurative, detergent,
   diuretic, dulling, easing, emetic, emollient, enema, expiatory,
   expurgatory, holystone, laxative, lenitive, lotion, lustral,
   lustrational, lustrative, mitigating, mitigative, mouthwash,
   nauseant, numbing, pain-killing, palliative, penitential, physic,
   piacular, propitiatory, pumice stone, purgatorial, purge, purging,
   purificatory, purifier, purifying, reclamatory, recompensing,
   redeeming, redemptive, redressing, relieving, remedial, reparative,
   reparatory, repentant, repenting, restitutional, restitutive,
   restitutory, righting, rinse, satisfactional, shampoo, soap,
   softening, solvent, soothing, squaring, subduing,
   synthetic detergent, tooth powder, toothpaste, wash