1. A noxious vapor or fog, especially one thought to cause disease or illness.
Usage: Historical: 19th-century medical theory attributed disease to bad air; now understood to be incorrect.; Often used figuratively in modern English.
2. A thick, oppressive, or unpleasant atmosphere or influence.
Usage: Figurative use; common in contemporary writing.

Examples

• Medieval doctors believed that miasma rising from swamps caused plague.
• A miasma of cigarette smoke hung over the crowded bar.
• The scandal left a miasma of distrust throughout the organization.
• The city's industrial district was shrouded in a thick miasma of smog.
• After the argument, a miasma of tension filled the room.
• Scientists eventually disproved the miasma theory of disease transmission.