WordNet (r) 3.0 (2006):

bowel movement
    n 1: a euphemism for defecation; "he had a bowel movement" [syn:
         bowel movement, movement, bm]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "bowel movement":
   BM, bloody flux, buffalo chips, ca-ca, catharsis, coprolite,
   coprolith, cow chips, cow flops, cow pats, crap, defecation,
   dejection, diarrhea, dingleberry, droppings, dung, dysentery,
   evacuation, feces, feculence, flux, guano, jakes, lientery,
   loose bowels, manure, movement, night soil, ordure, purgation,
   purge, runs, sewage, sewerage, shit, shits, stool, trots, turd,
   turistas, voidance