Sure to be specific (7)
I believe the answer is:
certain
This clue is a double definition.
'sure' is the first definition.
(synonyms)
'be specific' is the second definition.
(thesaurus)
'to' acts as a link.
(Other definitions for certain that I've seen before include "Proved beyond doubt" , "Indisputable" , "Assured" , "Absolutely sure" , "Convinced" .)