Talk idly about one freebooter (6)
I believe the answer is:
pirate
'freebooter' is the definition.
(I know that pirate is a type of freebooter)
'talk idly about one' is the wordplay.
'talk idly' becomes 'prate' (I've seen this in another clue).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'prate' going around 'i' is 'PIRATE'.
(Other definitions for pirate that I've seen before include "Bandit of the ocean, buccaneer" , "Sea-robber" , "fake" , "Illegally-copied (version)" , "plagiarist" .)