Source : Webster's Revised Unabridged Dictionary (1913)

Miasma \Mi*as"ma\, n.; pl. {Miasmata}. [NL., fr. Gr. ?
   defilement, fr. ? to pollute.]
   Infectious particles or germs floating in the air; air made
   noxious by the presence of such particles or germs; noxious
   effluvia; malaria.

Source : WordNet®

miasma
     n 1: an unwholesome atmosphere; "the novel spun a miasma of death
          and decay"
     2: unhealthy vapors rising from the ground or other sources;
        "the miasma of the marshes"; "a miasma of cigar smoke"
     [also: {miasmata} (pl)]