Other forms: unwelcomely
Things that are unwelcome are unpleasant or objectionable in some way. An unwelcome guest is one you didn't invite and you're not particularly happy to see.
People are sometimes unwelcome, like your boring cousin who shows up unexpectedly for a long visit at the worst time. Things can also be unwelcome, like bad news or heckling from the audience during your stand-up comedy routine. Anything you don't wish for and don't appreciate can be described as unwelcome. Welcome has its roots in the Old English wilcuma, a friendly greeting and earlier "a welcome guest," from willa, "pleasure or choice," and cuma, "guest."