Compounds of 上空

• 上空
  (n) sky
  the skies
  high-altitude sky
  upper air
  (P)
• 海上空港
  (n) seadrome
• 机上空論
  (n) impractical desktop theory (proposition)
  unworkable idea
  an idea that isn't worth the paper it's written on
• 史上空前
  (n) unprecedented in history
  unheard-of
  epoch-making