ab·struse 
(ăb-strs, əb-)
(ăb-strs, əb-)adj.
Difficult to understand; recondite: The students avoided the professor's abstruse lectures.
[Latin abstrūsus, past participle of abstrūdere, to hide : abs-, ab-, away; see AB-1 + trūdere, to push; see treud- in the Appendix of Indo-European roots.]
ab·strusely adv.
ab·struseness n.