rarefied
/ˈreərɪfaɪd/adjective
1- (of air, especially that at high altitudes) containing less oxygen than usual（空气, 尤指高海拔的空气）稀薄的; 稀疏的。
1.1
- figurative esoterically distant from the lives and concerns of ordinary people〈喻〉远离常人生活的; 怪异的：
debates about the nature of knowledge can seem very rarefied.
有关知识本质的辩论可能会显得深奥难解。