Source : Free On-Line Dictionary of Computing

nontrivial
     
        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 {uninteresting}, {interesting}.
     
        [{Jargon File}]
     
        (1995-02-21)