Etymology
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undesirable (adj.)

1660s, "not to be desired, objectionable," from un- (1) "not" + desirable. The noun meaning "undesirable person or thing" is first attested 1883. Undesired "not asked or invited" is recorded from late 15c.

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Definitions of undesirable
1
undesirable (adj.)
not wanted;
legislation excluding undesirable aliens
undesirable impurities in steel
Synonyms: unwanted
undesirable (adj.)
not worthy of being chosen (especially as a spouse);
Synonyms: unsuitable
2
undesirable (n.)
one whose presence is undesirable;
rounding up vagrants and drunks and other undesirables
From wordnet.princeton.edu