adj [usu attrib 通常作定语]
1 (of gases) less dense than is normal; thin （指气体）稀薄的
*the rarefied air (ie with little oxygen) of the Andes 安第斯山脉的稀薄空气（缺氧）.
2 (fig 比喻) (of ideas, etc) subtle and refined; lofty and exclusive （指思想等）缜密而纯正的, 清高的
*dons living in a rarefied academic atmosphere 生活在纯净的学术气氛中的大学教师.

adj [usually before noun]
a rarefied place, organization, or type of activity is only available to or understood by a small group of people - used to show disapproval
　the rarefied atmosphere of academia
rarefied air is the air in high places, which has less oxygen than usual