I'm undone, I'd fancy, and fading away (10)
I believe the answer is:
diminuendo
'fading away' is the definition.
(musical term)
'i'm undone i'd fancy' is the wordplay.
'fancy' is an anagram indicator.
'im'+'undone'+'id'='imundoneid'
'imundoneid' is an anagram of 'DIMINUENDO'.
'and' is the link.
(Other definitions for diminuendo that I've seen before include "volume is to be cut" , "Decrease in loudness" , "losing force" , "Making less sound" , "Letting sound fade away" .)