Word: Abstruse

You Pronounce It: [ab-stroos]

Definition: adjective
1. hard to understand; recondite; esoteric:
abstruse theories.
2. Obsolete. secret; hidden.

Origin: 1590-1600 Latin: abstrūsus thrust away, concealed (past participle of abstrūdere), equivalent to abs- abs- + trūd- thrust + -tus past participle suffix

I found it:

While reading, The Rhetorical Tradition: Readings from Classical Times to the Present by Bissell and Herzberg.

Works Cited:

http://www.dictionary.com/browse/abstruse