The Collaborative International Dictionary of English v.0.48:

Flatus \Fla"tus\, n.; pl. E. Flatuses, L. Flatus. [L., fr.
   flare to blow.]
   1. A breath; a puff of wind. --Clarke.
      [1913 Webster]

   2. Gas generated in the stomach, intestine, or other cavities
      of the body. --Quincy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flatus
    n 1: a reflex that expels intestinal gas through the anus [syn:
         fart, farting, flatus, wind, breaking wind]