strat·o·sphere 
(strătə-sfîr′)
(strătə-sfîr′)n.
1. The region of the atmosphere above the troposphere and below the mesosphere.
2. An extremely high or the highest point or degree on a ranked scale: business expenses in the stratosphere.
[French stratosphère : Latin strātus, a spreading out; see STRATUS + -sphère, sphere (from Old French espere; see SPHERE).]