Unsuitable, not fitting (13)
I believe the answer is:
inappropriate
This clue is a double definition.
'unsuitable' is the first definition.
(similar in meaning)
'not fitting' is the second definition.
(I've seen this before)
(Other definitions for inappropriate that I've seen before include "Improper" , "Out of keeping" , "unfit" , "Not fitting" , "This is misrepresented" .)