Trivial

Antonyms of trivial:
of import, serious, important, significant, adequate, effective, powerful, solid, useful, advantageous, efficient, profitable, sound, valid, beneficial, expedient, real, substantial, valuable, competent, potent, serviceable, sufficient, worthy, decisive, fatal, fateful, chief, dominant, overbearing, overmastering, overriding, principal, distinctive, exceptional, impressive, outstanding, prominent, remarkable, worthwhile, distinguished, eminent, great, illustrious, preeminent, prestigious, famous, notorious, renowned, all-important, basic, essential, fundamental, key, big, consequential, eventful, major, material, meaningful, momentous, unfrivolous, weighty, pivotal, conspicuous, noteworthy, striking, appreciable, discernible, measurable, considerable.
Examples of usage:
  1. Yet even if 1, 200 units of rotational momentum had been transferred to the orbital motion it would only correspond with the most trivial difference in the distance of Jupiter from the sun.
    "The Story of the Heavens", Robert Stawell Ball.
  2. This was not due to any extraordinary self- control on my part, for I was always ready to shed tears on the most trivial occasion.
    "The Ghost Ship", Richard Middleton.
  3. You do really carry too much expression, you take too intensely the trivial moments of life.
    "Increasing-Human-Efficiency-in-Business-a-contribution-to-the-psychology-of-business", Scott, Walter Dill.