The term 'unhealthy atmosphere' can be summarized by the 6-letter word MIASMA. MIASMA is a term used to describe an unhealthy or unpleasant atmosphere, usually caused by pollution or decay. It is often used to refer to a thick, visible fog or mist that contains pollutants and other harmful substances. In addition, MIASMA can also refer to a feeling of unease or dread that is created by an unhealthy environment.