[1] : The Collaborative International Dictionary of English v.0.48

abstruse \abstruse"\, a. l. abstrusus, p. p. of abstrudere to
   thrust away, conceal; ab, abs + trudere to thrust; cf. f.
   abstrus. see threat.
   1. concealed or hidden out of the way. obs.
      1913 webster

            the eternal eye whose sight discerns
            abstrusest thoughts.                  --milton.
      1913 webster

   2. remote from apprehension; difficult to be comprehended or
      understood; recondite; as, abstruse learning.
      1913 webster

            profound and abstruse topics.         --milman.
      1913 webster
see also:
threat 

[2] : WordNet (r) 2.0

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
see also:
deep recondite 

[3] : Moby Thesaurus II by Grady Ward, 1.0

102 moby thesaurus words for "abstruse":
   herculean, abstract, arcane, arduous, beclouded, blind, brutal,
   buried, civilized, close, clouded, complex, complicated, concealed,
   covered, covert, critical, cultivated, cultured, deep, delicate,
   demanding, difficile, difficult, eclipsed, educated, encyclopedic,
   erudite, esoteric, exacting, formidable, hairy, hard, hard-earned,
   hard-fought, heavy, hermetic, hid, hidden, hypothetical, ideal,
   in a cloud, in a fog, in eclipse, in purdah, in the wings,
   incommunicado, intricate, jawbreaking, knotted, knotty, laborious,
   latent, learned, lettered, literate, mean, mysterious, no picnic,
   not easy, obfuscated, obscure, obscured, occult, operose,
   pansophic, polyhistoric, polymath, polymathic, profound, recondite,
   rigorous, rough, rugged, scholarly, scholastic, secluded, secluse,
   secret, sequestered, set with thorns, severe, spiny, steep,
   strenuous, studious, thorny, ticklish, toilsome, tough,
   transcendental, tricky, under an eclipse, under cover,
   under house arrest, under wraps, underground, unknown, uphill,
   wicked, wise, wrapped in clouds

Abstruse >> A Words
Abstruse, definition of term: Abstruse
abstruse_pag1.html