Definition from Wiktionary, the free dictionary
- objectionable or not likely to please
Usage notes 
- Nouns to which "undesirable" is often applied: effect, consequence, result, element, change, person, substance, characteristic, quality, feature, behavior, activity, thing, event, reaction, state.
objectionable or not likely to please
undesirable (plural undesirables)
- an undesirable person