gordian \GOR-dee-uhn\ (adjective) - Highly intricate; extremely difficult to solve.
"All agreed that coming up with a solution to the gordian problem of where to locate the company's new branch office was certain to take everyone's full attention for quite some time."
In Greek mythology, King Gordius of Phrygia tied a knot that defied all who tried to untie it. An oracle prophesied that one who would undo this Gordian knot would rule Asia. Alexander the Great simply cut the knot with one stroke of his sword. Hence the saying, "to cut the Gordian knot" meaning to solve a difficult problem by a simple, bold, and effective action.