Not likely to please; objectionable: undesirable intrusions.
Not wanted: undesirable aliens.
n. A person regarded as undesirable: "men tentatively regarded as scoundrels—or at least as undesirables"(New York). un'de·sir'a·bil'i·ty n., un'de·sir'a·bly adv.
1667, "not to be desired, objectionable," from un- (1) "not" + desire + -able. The noun meaning "undesirable person or thing" is first attested 1883. Undesired "not asked or invited" is recorded from 1470.