Because a music centre can be nice? (5)
I believe the answer is:
since
'because' is the definition.
(thesaurus)
'a music centre can be nice?' is the wordplay.
'centre' means to look at the middle letters.
'can be' indicates an anagram.
The centre of 'music' is 's'.
'nice' anagrammed 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" .)