n.

1. 【氣】同溫層；平流層
2. 最上層
3. 尖端（或深奧）的學科領域

n.

1. the layer of the earth's atmosphere above the troposphere, extending to about 50 km above the earth's surface (the lower boundary of the mesosphere).
2. informal the very highest levels of something:
   the fashion stratosphere.