abstruse
Word family adverbabstruselyadjectiveabstrusenounabstruseness
ab·struse /əbˈstruːs, æb-/ adjectiveadj formal COMPLICATEDunnecessarily complicated and difficult to understand 深奥的，高深的 Maths is a mix of abstruse theory and detailed calculations. 数学既有深奥的理论，又有精密的计算。
(1500-1600) Latin past participle of abstrudere “to hide”, from abs- “away” + trudere “to push”