noun

1. the gaseous envelope (air) surrounding the earth to a height of c. 1,000 km (c. 621 mi): it is c. 21% oxygen, 78% nitrogen, and 1% other gases, and rotates with the earth, because of gravity
2. the gaseous mass surrounding any star, planet, etc.
3. the air in any given place
4. a pervading or surrounding influence or spirit; general mood or social environment
5. the general tone of a work of art a play with a fateful atmosphere
6. Informal an interesting, often exotic, effect produced by decoration, furnishings, etc. a restaurant with atmosphere
7. Physics a standard unit of pressure used to measure atmospheric pressure, equal to the pressure exerted by a column of mercury that is 760 millimeters (29.9213 inches) high at 0°C at sea level (101,325 pascals or 1,013.25 millibars or 14.70 pounds per square inch): abbrev. atm

Etymology: ModL atmosphaera < Gr atmos, vapor + sphaira, sphere