Curt and I composed a song ... Nettlerash (9)
I believe the answer is:
urticaria
'nettlerash' is the definition.
(I've seen this before)
'curt and i composed a song' is the wordplay.
'and' is a charade indicator (letters next to each other).
'composed' indicates an anagram.
'a song' becomes 'aria' (aria is a kind of song).
'curt' put after 'i' is 'icurt'.
'icurt' with letters rearranged gives 'urtic'.
'urtic'+'aria'='URTICARIA'
(Other definitions for urticaria that I've seen before include "hives" , "Nettle rash" , "complaint" , "Nettlerash" .)