adj. 25B6; adjective
undesirable side effects : UNPLEASANT, disagreeable, nasty, unwelcome, unwanted, unfortunate, infelicitous.
some very undesirable people : UNPLEASANT, disagreeable, obnoxious, nasty, awful, terrible, dreadful, frightful, repulsive, repellent, abhorrent, loathsome, hateful, detestable, deplorable, appalling, insufferable, intolerable, despicable, contemptible, odious, vile, unsavoury; informal ghastly, horrible, horrid; Brit. informal beastly.
pleasant, agreeable.