Mac Dictionary’s definition:
The envelope of gases surrounding the earth or another planet : part of the sun’s energy is absorbed by the earth’s atmosphere.
• the air in any particular place : we couldn’t breathe in the dusty atmosphere of his apartment.
• (abbr.: atm) Physics a unit of pressure equal to mean atmospheric pressure at sea level, 101,325 pascals.
2 the pervading tone or mood of a place, situation, or work of art : the hotel is famous for its friendly, welcoming atmosphere | this crisis further compounded the prevailing atmosphere of gloom.
• a pleasurable and interesting or exciting mood : a superb restaurant, full of atmosphere.
ORIGIN mid 17th cent.: from modern Latin atmosphaera, from Greek atmos ‘vapor’ + sphaira ‘ball, globe.’