Quirk (12)
There are a few possibilities for this:
idiosyncrasy
'quirk' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for idiosyncrasy that I've seen before include "Foible" , "Quirk" , "Distinctive mannerism" , "Distinctive or peculiar characteristic" , "Peculiarity" .)
'quirk' is the definition.
(I know that quirk can be written as oddity)
This is all the clue.
(Other definitions for oddity that I've seen before include "Peculiarity" , "Something peculiar, person or event" , "Something unusual or curious" , "Something strange or eccentric" , "Curio, rarity" .)
'quirk' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for foible that I've seen before include "weakness" , "Minor eccentricity" , "Harmless peculiarity or mannerism" , "'Mannerism, idiosyncrasy (6)'" , "Harmless peculiarity in person's character" .)