Prior use changed for better (8)
I believe the answer is:
superior
'better' is the definition.
(thesaurus)
'prior use changed' is the wordplay.
'changed' indicates an anagram.
'prior'+'use'='prioruse'
'prioruse' is an anagram of 'SUPERIOR'.
'for' is the link.
(Other definitions for superior that I've seen before include "The largest of the Great Lakes" , "Snooty" , "Classy" , "Higher in position or rank" , "Mother is sometimes" .)