atmosphere

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The gaseous mass or envelope surrounding a celestial body, especially the one surrounding the earth, and retained by the celestial body's gravitational field.
• noun The air or climate in a specific place.
• noun 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).
• noun A dominant intellectual or emotional environment or attitude.
• noun The dominant tone or mood of a work of art.
• noun An aesthetic quality or effect, especially a distinctive and pleasing one, associated with a particular place.

from The Century Dictionary.

• noun The aëriform fluid which surrounds the earth, and extends to an undetermined height above its surface; the air.
• noun A conventional unit of atmospheric pressure.
• noun The gaseous envelop surrounding any of the heavenly bodies.
• noun Any gaseous medium: as, “an atmosphere of cold oxygen,” Miller.
• noun An assumed outer envelop of force, effluvia, etc., surrounding a body: as, an electrical atmosphere.
• noun Figuratively, intellectual or moral environment; pervading influence.

from the GNU version of the Collaborative International Dictionary of English.

• noun The whole mass of aëriform fluid surrounding the earth; -- applied also to the gaseous envelope of any celestial orb, or other body.
• noun Any gaseous envelope or medium.
• noun A supposed medium around various bodies.
• noun The pressure or weight of the air at the sea level, on a unit of surface, or about 14.7 lbs. to the sq. inch.
• noun Any surrounding or pervading influence or condition.
• noun The portion of air in any locality, or affected by a special physical or sanitary condition

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The gases surrounding the Earth or any astronomical body.
• noun The air in a particular place.
• noun The mood or feeling in a situation.
• noun A unit of measurement for pressure (symbol: atm)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the mass of air surrounding the Earth
• noun a distinctive but intangible quality surrounding a person or thing
• noun a particular environment or surrounding influence
• noun the envelope of gases surrounding any celestial body
• noun the weather or climate at some place
• noun a unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade