Sharpens edge of bolt that’s blunt (6)
I believe the answer is:
honest
'blunt' is the definition.
(blunt can mean honest or frank)
'sharpens edge of bolt' is the wordplay.
'sharpens' becomes 'hones' (honing is a kind of sharpening).
'edge of' says to take the final letters (one of the letters on the edge of the word).
The last letter of 'bolt' is 't'.
'hones'+'t'='HONEST'
'that's' acts as a link.
(Other definitions for honest that I've seen before include "Not cheating, just" , "Impartial intermediary" , "Fair and square" , "Objective mediator" , "Trustworthy or candid" .)