A habit isn't something she's accustomed to (6)
I believe the answer is:
nudist
'accustomed to' is the definition.
Although both the answer and definition are adjectives, I can't see how one could define the other.
'a habit isn't something she's' is the wordplay.
I cannot quite see how this works, but
'she's' could be 'dis' and 'dis' is present in the answer.
The remaining letters 'nut' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for nudist that I've seen before include "One going unclothed" , "one whose barely seen" , "Person who goes around unclothed" , "Someone choosing not to wear clothes" , "He thinks clothes unhealthy" .)