nontrivial

nonlinear | = N = | not entirely unlike X

nontrivial adj.

Requiring real thought or significant computing power. Often used as an understated way of saying that a problem is quite difficult or impractical, or even entirely unsolvable ("Proving P=NP is nontrivial"). The preferred emphatic form is `decidedly nontrivial'. See trivial, uninteresting, interesting.

nonlinear | = N = | not entirely unlike X