Wind up with a closing passage (4)
I believe the answer is:
coda
'closing passage' is the definition.
(I've seen this before)
'wind up with a' is the wordplay.
'wind' becomes 'doc' (I am not sure about this - if you are sure you should believe this answer much more).
'up' is a reversal indicator (in down clue: letters go upwards).
'with' says to put letters next to each other.
'doc' reversed gives 'cod'.
'cod'+'a'='CODA'
Can you help me to learn more?
(Other definitions for coda that I've seen before include "Concluding passage of a musical composition" , "Closing bars (mus.)" , "Musical finale" , "finale in Beethoven?" , "Closing passage of a piece of music" .)