Frank is unaffected (7)
I believe the answer is:
natural
I believe this is a double definition.
'frank' is the first definition.
(thesaurus)
'unaffected' is the second definition.
('natural' can be a synonym of 'unaffected')
'is' is the link.
(Other definitions for natural that I've seen before include "Unaffected - innate" , "Not artificial or affected" , "Not made; off-white" , "Inborn; unaffected" , "Genuine, unaffected" .)