Approve of American fashion (4)
I believe the answer is:
okay
'approve' is the definition.
(I know that approve can be written as okay)
'of american fashion' is the wordplay.
'of' becomes 'o''.
'american fashion' becomes 'kay' (I can't explain this - if you can you should believe this answer much more).
'o'+'kay'='OKAY'
Can you help me to learn more?
(Other definitions for okay that I've seen before include "Alright" , "Permissible (colloq.)" , "Give approval to" , "Informally, all right" , "Authorise" .)