Noxious exhalations from putrescent organic matter; poisonous effluvia or germs polluting the atmosphere. (Dictionary.com)
A dangerous, foreboding, or deathlike influence or atmosphere. (Dictionary.com)
Producing an unpleasant smell; noxious. (Oxford Dictionaries)
Characterised by a mysterious and unpleasant atmosphere; oppressive. (Oxford Dictionaries)
A vaporous exhalation formerly believed to cause disease. (Merriam -Webster)
An influence or atmosphere that tends to deplete or corrupt. (Merriam – Webster)
Miasma theory. Science Museum. Brought to life.
Miasma. Plague. flickr.