The Collaborative International Dictionary of English v.0.48:

BM \BM\ n.
   an abbreviation for bowel movement; -- used as an informal
   euphemism, especially in hospitals. [informal, abbrev.]
   [PJC]

WordNet (r) 3.0 (2006):

BM
    n 1: solid excretory product evacuated from the bowels [syn:
         fecal matter, faecal matter, feces, faeces, BM,
         stool, ordure, dejection]
    2: 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 "BM":
   bloody flux, bowel movement, 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



The Free On-line Dictionary of Computing (30 December 2018):

bm

    The country code for Bermuda.

   (1999-01-27)