Truthful, frank (6)
I believe the answer is:
candid
I believe this clue is a double definition.
'truthful' is the first definition.
(I've seen this before)
'frank' is the second definition.
(I know that frank can be written as candid)
(Other definitions for candid that I've seen before include "Frank, forthright" , "Frank and outspoken" , "Forthrightly sincere" , "Impartial" , "Honest and open about what one thinks" .)