The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]