abstruse

adj. ambiguous, difficult to understand obscure

Adjective
1. difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge; "the professor's lectures were so abstruse that students tended to avoid them"; "a deep metaphysical theory"; "some recondite problem in historiography"
(synonym) deep, recondite
(similar) esoteric

adj. abstruse, obscure; fanciful, wild, strange; imaginary; unreal; whimsical

adj. abstruse, ambiguous; recondite, profound, relatively unknown

(a.)
Remote from apprehension; difficult to be comprehended or understood; recondite; as, abstruse learning.
  

(a.)
Concealed or hidden out of the way.