1) abstruse
[英][əb'stru:s] [美][əb'strus]

深奥
1.
The knowledge about the words in classical Chinese is complicated and abstruse,in Junior Chinese book the same word has different meanings between the classical Chinese and Today s.
文言文知识是复杂而深奥的,了解古今字与通假字的有关知识,分清初中课本中的古今字与通假字,对将来进入高一级学校及其今后的学习有极大帮助。
2) profundity
[英][prə'fʌndəti] [美][prə'fʌndətɪ]

深;深远;深奥;深刻