To be frank, not keen

I believe the answer is:

blunt

I'm a little stuck... Click here to teach me more about this clue!

'to be frank' is the definition.
(synonyms)

'not keen' is the wordplay.
I cannot really see how this works, but
'not' could be 'nt' (synonyms) and 'nt' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for blunt that I've seen before include "not cutting" , "Not sharp; forthright" , "Forthright - Soviet spy" , "To the point; without point" , "Lacking edge; forthright" .)

I've seen this clue in the Evening Standard.

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