(1) A distinctive but intangible quality surrounding a person or thing
"An air of mystery"
"The house had a neglected air"
"An atmosphere of defeat pervaded the candidate's headquarters"
"The place had an aura of romance"
(2) The mass of air surrounding the Earth
"There was great heat as the comet entered the atmosphere"
"It was exposed to the air"
(3) The envelope of gases surrounding any celestial body
(4) A unit of pressure: the pressure that will support a column of mercury 760 mm high at sea level and 0 degrees centigrade
(5) The weather or climate at some place
"The atmosphere was thick with fog"
(6) A particular environment or surrounding influence
"There was an atmosphere of excitement"