'BM' definitions:

Definition of 'BM'

From: WordNet
noun
Solid excretory product evacuated from the bowels [syn: fecal matter, faecal matter, feces, faeces, BM, stool, ordure, dejection]
noun
A euphemism for defecation; "he had a bowel movement" [syn: bowel movement, movement, bm]

Definition of 'BM'

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