Furious, heading off buccaneer (5)
I believe the answer is:
irate
'furious' is the definition.
(thesaurus)
'heading off buccaneer' is the wordplay.
'heading off' means to remove the first letter.
'buccaneer' becomes 'pirate' ('pirate' can be a synonym of 'buccaneer').
'pirate' with its first letter removed is 'IRATE'.
(Other definitions for irate that I've seen before include "Annoyed, exasperated" , "ranting" , "will be up in arms" , "Hacked off" , "Extremely cross" .)