Suit: fine one, choice clothes (5)
I believe the answer is:
befit
'suit' is the definition.
(I know that suit can be written as befit)
'fine one choice clothes' is the wordplay.
'fine' becomes 'f' (abbreviation in pencil classifications).
'one choice' becomes 'beit' (I am not sure about this - if you are sure you should believe this answer much more).
'clothes' indicates putting letters inside (some letters clothe or cover others).
'f' placed into 'beit' is 'BEFIT'.
Can you help me to learn more?
(Other definitions for befit that I've seen before include "Be right and suitable for" , "Be appropriate for" , "Become, suit" .)