1660s, from Modern Latin miasma "noxious vapors," from Greek miasma (genitive miasmatos) "stain, pollution, defilement, taint of guilt," from stem of miainein "to pollute," from possible PIE root *mai- "to stain, soil, defile" (source of Old English mal "stain, mark," see mole, n.1). Earlier form was miasm (1640s), from French miasme. Related: Miasmatic; miasmal.