The Collaborative International Dictionary of English v.0.48:

Inconsiderable \In`con*sid"er*a*ble\, a.
   Not considerable; unworthy of consideration or notice;
   unimportant; small; trivial; as, an inconsiderable distance;
   an inconsiderable quantity, degree, value, or sum. "The baser
   scum and inconsiderable dregs of Rome." --Stepney. --
   In`con*sid"er*a*ble*ness, n. -- In`con*sid"er*a*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inconsiderable
    adj 1: too small or unimportant to merit attention; "passed his
           life in an inconsiderable village"; "their duties were
           inconsiderable"; "had no inconsiderable influence" [ant:
           considerable]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "inconsiderable":
   back-burner, cursory, depthless, dinky, dispensable, few, footling,
   immaterial, inappreciable, inconsequential, inessential, inferior,
   insignificant, irrelevant, little, low, meager, miniature, minor,
   minute, negligible, no great shakes, nonessential, not vital,
   petit, petty, picayune, picayunish, shallow, short, skin-deep,
   small, superficial, technical, tiny, trifling, trivial,
   unessential, unimpressive, unnoteworthy