1) Close 2) Hermetically sealed 3) Lacking air 4) Lacking atmosphere 5) Lacking fresh air 6) Like a vacuum 7) Like a vacuum or the moon 8) Like the moon 9) Needing ventilation 10) Stuffy 11) That is without a breeze 12) That is without fresh air 13) Unaired 14) Unventilated 15) Without oxygen 1) Flat 2) Hot 3) Stuffy 4) Unaired 5) Unventilated 
• (a.) Not open to a free current of air; wanting fresh air, or communication with the open air.
Air'less adjective Not open to a free current of air; wanting fresh air, or communication with the open air. 
[adj] - lacking fresh air
close adjective lacking fresh air; `a dusty airless attic`; `the dreadfully close atmosphere`; `hot and stuffy and the air was blue with smoke`
lacking air. · that is without fresh air; stuffy: a dark, airless hallway. · that is without a breeze; still: an airless July day.