noun.
A poisonous atmosphere formerly thought to rise from swamps and putrid matter and cause disease.
noun.
A thick vaporous atmosphere or emanation.
The Century Dictionary and Cyclopedia
noun.
The emanations or effluvia arising from the ground and floating in the atmosphere, considered to be infectious or otherwise injurious to health; noxious emanations; malaria. Also called aërial poison.
the GNU version of the Collaborative International Dictionary of English
noun.
Infectious particles or germs floating in the air; air made noxious by the presence of such particles or germs; noxious effluvia; malaria.