Source : Webster's Revised Unabridged Dictionary (1913)

Effluvium \Ef*flu"vi*um\, n.; pl. {Effluvia}. [L., a flowing
   out, fr. effluere to flow out. See {Effluent}, a.]
   Subtile or invisible emanation; exhalation perceived by the
   sense of smell; especially, noisome or noxious exhalation;
   as, the effluvium from diseased or putrefying bodies, or from
   ill drainage.

Source : WordNet®

effluvium
     n : a foul-smelling outflow or vapor (especially a gaseous
         waste)
     [also: {effluvia} (pl)]