He's all dressed up - fine for an American (5)
I believe the answer is:
dandy
'an american' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'he's all dressed up fine' is the wordplay.
'he' becomes 'Dan'.
'all dressed up fine' becomes 'dy' (I can't justify this - if you can you should give a lot more credence to this answer).
'dan'+'dy'='DANDY'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for dandy that I've seen before include "Beau" , "See 6" , "comic, 1937-2012" , "Playboy" , "Foppish man" .)