Sister having nothing to say (3)
I believe the answer is:
nun
'sister' is the definition.
(thesaurus)
'nothing to say' is the wordplay.
'nothing' becomes 'none' (I've seen this before).
'to say' shows a homophone (sound like).
'none' is a homophone of 'NUN'.
'having' acts as a link.
(Other definitions for nun that I've seen before include "Religious woman, a palindrome" , "A palindromic lady in religious order" , "A palindromic holy woman" , "religious person" , "Religious sister" .)