Music is nothing to a Manx cat (4)
I believe the answer is:
opus
'music' is the definition.
(opus is a kind of music)
'nothing to a manx cat' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'to a manx' means to remove the last letter (Manx cats have no tail).
'cat' becomes 'puss' (puss is a kind of cat).
'puss' with its last letter taken off is 'pus'.
'o'+'pus'='OPUS'
'is' is the link.
(Other definitions for opus that I've seen before include "Major work" , "Soup (anag.)" , "Musical composition in the soup" , "(Numbered) musical composition" , "Work of 25 perhaps" .)