Music means nothing to a Manx cat (4)
I believe the answer is:
opus
'music' is the definition.
(I know that opus is a type 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 (the word has no 'tail', like a Manx cat).
'cat' becomes 'puss' (puss is a kind of cat).
'puss' with its final letter removed is 'pus'.
'o'+'pus'='OPUS'
'means' acts as a link.
(Other definitions for opus that I've seen before include "Work (of a composer?)" , "Artistic work" , "Creative work, eg in writing, art or music" , "Major work" , "Work or composition, usually musical" .)