Frank is able - and proved it (6)
I believe the answer is:
candid
'frank' is the definition.
(synonyms)
'able and proved it' is the wordplay.
I cannot quite understand how this works, but
'able' could be 'can' and 'can' is present in the answer.
The remaining letters 'did' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for candid that I've seen before include "Truthful, frank" , "Frank, forthright" , "Open and truthful" , "Frank - unbiased" , "Frank and outspoken" .)