The Collaborative International Dictionary of English v.0.48:

Trivial \Triv"i*al\, a. [L. trivialis, properly, that is in, or
   belongs to, the crossroads or public streets; hence, that may
   be found everywhere, common, fr. trivium a place where three
   roads meet, a crossroad, the public street; tri- (see Tri-)
   + via a way: cf. F. trivial. See Voyage.]
   1. Found anywhere; common. [Obs.]
      [1913 Webster]

   2. Ordinary; commonplace; trifling; vulgar.
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            As a scholar, meantime, he was trivial, and
            incapable of labor.                   --De Quincey.
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   3. Of little worth or importance; inconsiderable; trifling;
      petty; paltry; as, a trivial subject or affair.
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            The trivial round, the common task.   --Keble.
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   4. Of or pertaining to the trivium.
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   Trivial name (Nat. Hist.), the specific name.
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The Collaborative International Dictionary of English v.0.48:

Trivial \Triv"i*al\, n.
   One of the three liberal arts forming the trivium. [Obs.]
   --Skelton. Wood.
   [1913 Webster]

WordNet (r) 3.0 (2006):

trivial
    adj 1: (informal) small and of little importance; "a fiddling
           sum of money"; "a footling gesture"; "our worries are
           lilliputian compared with those of countries that are at
           war"; "a little (or small) matter"; "a dispute over
           niggling details"; "limited to petty enterprises";
           "piffling efforts"; "giving a police officer a free meal
           may be against the law, but it seems to be a picayune
           infraction" [syn: fiddling, footling, lilliputian,
           little, niggling, piddling, piffling, petty,
           picayune, trivial]
    2: of little substance or significance; "a few superficial
       editorial changes"; "only trivial objections" [syn:
       superficial, trivial]
    3: concerned with trivialities; "a trivial young woman"; "a
       trivial mind"

Moby Thesaurus II by Grady Ward, 1.0:

111 Moby Thesaurus words for "trivial":
   Mickey, NG, airy, ankle-deep, asinine, base, bickering, captious,
   casual, catchpenny, caviling, cheap, choplogic, cursory, deficient,
   depthless, empty, epidermal, equivocatory, evasive, fatuous, few,
   flimsy, foolish, footling, fribble, fribbling, frivolous, frothy,
   futile, good-for-naught, good-for-nothing, hairsplitting, hedging,
   idle, imperfect, inadequate, inane, incompetent, inconsequential,
   inconsiderable, insignificant, insufficient, jejune, junk, junky,
   knee-deep, light, little, logic-chopping, low, maladroit, meager,
   mean, measly, mediocre, miniature, minor, negligible, nit-picking,
   no great shakes, no-account, no-good, not comparable, not deep,
   not in it, not worth having, not worth mentioning, not worthwhile,
   nugacious, nugatory, on the surface, otiose, out of it, paltering,
   petty, picayune, picayunish, pussyfooting, quibbling, shabby,
   shallow, shallow-rooted, shoal, shoddy, shoestring, short,
   shuffling, silly, skin-deep, slender, slight, small, small-beer,
   superficial, surface, thin, tiny, trashy, trichoschistic, trifling,
   trite, unimportant, unprofound, unskillful, vacuous, vain,
   valueless, vapid, windy, worthless



The Jargon File (version 4.4.7, 29 Dec 2003):

trivial
 adj.

    1. Too simple to bother detailing.

    2. Not worth the speaker's time.

    3. Complex, but solvable by methods so well known that anyone not utterly 
    cretinous would have thought of them already.

    4. Any problem one has already solved (some claim that hackish trivial
    usually evaluates to ?I've seen it before?). Hackers' notions of triviality
    may be quite at variance with those of non-hackers. See nontrivial, 
    uninteresting.

    The physicist Richard Feynman, who had the hacker nature to an amazing
    degree (see his essay ?Los Alamos From Below? in Surely You're Joking, Mr.
    Feynman!), defined trivial theorem as ?one that has already been proved?.


Bouvier's Law Dictionary, Revised 6th Ed (1856):

TRIVIAL. Of small importance. It is a rule in equity that a demurrer will
lie to a bill on the ground of the triviality of the matter in dispute, as
being below the dignity of the court. 4 Bouv. Inst. n. 4237. See Hopk. R.
112; 4 John. Ch. 183; 4 Paige, 364.