ab·struse /əbˈstrus, æb-/
  (a.)難解的,深奧的
  Ab·struse a.
  1. Concealed or hidden out of the way. [Obs.]
  The eternal eye whose sight discerns
  Abstrusest thoughts.   --Milton.
  2. Remote from apprehension; difficult to be comprehended or understood; recondite; as, abstruse learning.
     Profound and abstruse topics.   --Milman.
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  abstruse
       adj : 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" [syn: deep, recondite]