The Collaborative International Dictionary of English v.0.48:

Undistinguished \Undistinguished\
   See distinguished.

WordNet (r) 3.0 (2006):

undistinguished
    adj 1: not worthy of notice [syn: insignificant,
           undistinguished]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "undistinguished":
   alike, common, commonplace, everyday, homely, homespun, humble,
   humble-looking, humble-visaged, humblest, ignotus, indifferent,
   indiscernible, indistinct, indistinctive, indistinguishable,
   inglorious, innocuous, interchangeable, least, little known, low,
   lowest, lowliest, lowly, mean, mediocre, middling, modest,
   nameless, no credit to, no great shakes, obscure, ordinary,
   pedestrian, plain, poor, prosaic, renownless, run-of-the-mill,
   simple, small, so so, standard, stereotyped, teachable,
   uncelebrated, undifferentiated, undiscriminated, undistinguishable,
   unexceptional, unexciting, unfamed, unglorified, unheard-of,
   unhonored, uniform, unimportant, unimpressive, unknown, unnotable,
   unnoted, unnoticed, unpopular, unpretentious, unremarkable,
   unremarked, unrenowned, unsung, without distinction