Adjective

(en-adj)

(obsolete) Concealed or hidden out of the way; secret.

* 1612 , Thomas Shelton (translator), Miguel de Cervantes (Spanish author), The History of the Valorous and Wittie Knight-Errant Don-Quixote of the Mancha , Part 4, Chapter 15, page 500:

O who is he that could carrie newes to our olde father, that thou wert but aliue, although thou wert hidden in the most abstruse dungeons of Barbarie; for his riches, my brothers and mine would fetch thee from thence.

* 1667 , , Paradise Lost :

The eternal eye whose sight discerns abstrusest thoughts.

Difficult to comprehend or understand; recondite; obscure; esoteric.

* 1548 , Bishop John Hooper, A Declaration of the Ten Holy Comaundementes of Almygthye God , Chapter 17 Curiosity, Page 218:

...at the end of his cogitacions, fyndithe more abstruse , and doutfull obiections then at the beginning...

* 1748 , David Hume, Enquiries concerning the human understanding and concerning the principles of moral. London: Oxford University Press, 1973. § 13.

It is certain that the easy and obvious philosophy will always, with the generality of mankind, have the preference above the accurate and abstruse ;

* 1855 , , History of Latin Christianity :

Profound and abstruse topics.

Adjective

(en adjective)

Hard, not easy, requiring much effort.

* (Nathaniel Hawthorne) (1804-1864)

There is not the strength or courage left me to venture into the wide, strange, and difficult world, alone.

* 2008 , Daniel Goleman, Destructive Emotions: A Scientific Dialogue with the Dalai Lama (ISBN 0307483762), page 199:

In adults, the same kind of anger has been studied in people trying to solve a very difficult math problem. Though the tough math problem is very frustrating, there is an active attempt to solve the problem and meet the goal.

* {{quote-magazine, date=2013-08-03, volume=408, issue=8847, magazine=(The Economist)

, title= Boundary problems , passage=Economics is a messy discipline: too fluid to be a science, too rigorous to be an art. Perhaps it is fitting that economists’ most-used metric, gross domestic product (GDP), is a tangle too.

Hard to manage, uncooperative, troublesome.