Source : WordNet®

undesirable
     adj 1: not desirable; "undesirable impurities in steel";
            "legislation excluding undesirable aliens" [ant: {desirable}]
     2: not worthy of being chosen (especially as a spouse) [syn: {unsuitable}]
     n : one whose presence is undesirable; "rounding up vagrants and
         drunks and other undesirables"