Candid, frank (4)
I believe the answer is:
open
This clue is a double definition.
'candid' is the first definition.
(I know that candid can be written as open)
'frank' is the second definition.
(synonyms)
(Other definitions for open that I've seen before include "Affording access" , "Widely known" , "Traditional room heater" , "Not shut or secret" , "Not enclosed" .)