1. The gaseous mass or envelope surrounding a celestial body, especially the one surrounding the earth, and retained by the celestial body's gravitational field.
2. The air or climate in a specific place.
3. (Abbr. atm) Physics. A unit of pressure equal to the air pressure at sea level. It equals the amount of pressure that will support a column of mercury 760 millimeters high at 0 degrees Celsius under standard gravity, or 14.7 pounds per square inch (1.01325 × 10⁵ pascals).
4. A dominant intellectual or emotional environment or attitude: an atmosphere of distrust among the electorate.
5. The dominant tone or mood of a work of art.
6. An aesthetic quality or effect, especially a distinctive and pleasing one, associated with a particular place: a restaurant with an Old World atmosphere.

[New Latin atmosphaera : Greek atmos, vapor + Latin sphaera, sphere; see sphere.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.