Talk foolishly about one buccaneer (6)
I believe the answer is:
pirate
'buccaneer' is the definition.
(historical term for a pirate)
'talk foolishly about one' is the wordplay.
'talk foolishly' becomes 'prate' (to prate is to talk nonsense).
'about' indicates putting letters inside.
'one' becomes 'I' (Roman numeral).
'prate' enclosing 'i' is 'PIRATE'.
(Other definitions for pirate that I've seen before include "Use (another's work) for profit without permission" , "Bandit of the ocean, buccaneer" , "Sea-robber" , "Illegal" , "fake" .)