Because a music centre can be nice? (5)
I believe the answer is:
since
'because' is the definition.
('since' can mean 'because')
'a music centre can be nice?' is the wordplay.
'centre' indicates the central letters.
'can be' indicates anagramming the letters.
The centre of 'music' is 's'.
'nice' with letters rearranged gives 'ince'.
's'+'ince'='SINCE'
(Other definitions for since that I've seen before include "Seeing that" , "in the past" , "Because; ago" , "From that time one" .)