Nominally honest (5)
I believe the answer is:
frank
'honest' is the definition.
(similar in meaning)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for frank that I've seen before include "Anne ---, diarist" , "Open" , "Old German" , "Without evasion" , "Candid, honest" .)