The Collaborative International Dictionary of English v.0.48:

Undisturbed \Undisturbed\
   See disturbed.

WordNet (r) 3.0 (2006):

undisturbed
    adj 1: untroubled by interference or disturbance; "he could
           pursue his studies undisturbed"

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "undisturbed":
   at rest, calm, cloistered, cool, dwindling, ebbing, even-tenored,
   halcyon, hushed, impassive, isolated, moldering, pacific,
   peaceable, peaceful, placid, quiescent, quiet, reposeful, reposing,
   restful, resting, secluded, sequestered, sequestrated, sheltered,
   smooth, still, still as death, stillish, stilly, stoic, stolid,
   subsiding, tranquil, unagitated, unbothered, unexcited,
   unflustered, unimpassioned, unmoved, unperturbed, unplagued,
   unruffled, unstirred, unstirring, untormented, untroubled, unvexed,
   unworried, waning