The Collaborative International Dictionary of English v.0.48:

Uncomfortable \Un*com"fort*a*ble\, a.
   1. Feeling discomfort; uneasy; as, to be uncomfortable on
      account of one's position.
      [1913 Webster]

   2. Causing discomfort; disagreeable; unpleasant; as, an
      uncomfortable seat or situation.
      [1913 Webster]

            The most dead, uncomfortable time of the year.
                                                  --Addison.
      [1913 Webster] -- Un*com"fort*a*ble*ness, n. --
      Un*com"fort*a*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

uncomfortable
    adj 1: conducive to or feeling mental discomfort; "this kind of
           life can prove disruptive and uncomfortable"; "the
           uncomfortable truth"; "grew uncomfortable beneath his
           appraising eye"; "an uncomfortable way of surprising me
           just when I felt surest"; "the teacher's presence at the
           conference made the child very uncomfortable" [ant:
           comfortable]
    2: providing or experiencing physical discomfort; "an
       uncomfortable chair"; "an uncomfortable day in the hot sun"
       [ant: comfortable, comfy]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "uncomfortable":
   abashed, affecting, afflicted, afflictive, agitated, beset, bitter,
   bleak, bothered, cast down, chagrined, chapfallen, cheerless,
   comfortless, confused, deplorable, depressing, depressive,
   discomfited, discomforted, discomforting, discomposed,
   disconcerted, dismal, dismaying, disquieted, distressed,
   distressful, distressing, disturbed, dolorific, dolorogenic,
   dolorous, dreary, embarrassed, grievous, harsh, hung up,
   ill at ease, joyless, lamentable, mortified, mournful, moving,
   out of countenance, painful, pathetic, perturbed, piteous,
   pitiable, poignant, put-out, put-upon, regrettable, rueful, sad,
   saddening, sharp, sore, sorrowful, touching, troubled, uneasy,
   upset, woebegone, woeful, wretched