The Collaborative International Dictionary of English v.0.48:

Unwelcome \Unwelcome\
   See welcome.

WordNet (r) 3.0 (2006):

unwelcome
    adj 1: not welcome; not giving pleasure or received with
           pleasure; "unwelcome publicity"; "unwelcome
           interruptions"; "unwelcome visitors" [ant: welcome]
    2: not welcome; "unwelcome publicity" [syn: unwelcome,
       unwished, unwished-for]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "unwelcome":
   anathema, bitter, disagreeable, dislikable, displeasing,
   distasteful, exceptionable, excluded, ill-favored, inadmissible,
   obnoxious, persona non grata, rejected, repellent, sour, thankless,
   ugly, unacceptable, unaccepted, unagreeable, unalluring,
   unappealing, unappetizing, unasked, unasked-for, unattractive,
   unbidden, uncalled-for, undelectable, undelicious, undesirable,
   undesired, unengaging, unenjoyable, uninvited, uninviting,
   unlikable, unpalatable, unpleasant, unpleasing, unsavory, unsought,
   untasteful, unwanted, unwished