Person being disloyal or missing characteristic (5)
I believe the answer is:
trait
'characteristic' is the definition.
(I've seen this in other clues)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for trait that I've seen before include "Feature of personality" , "Mannerism" , "Decorative band" , "Habit" , "Characteristic or distinguishing quality" .)