Furious corsair loses head (5)
I believe the answer is:
irate
'furious' is the definition.
(thesaurus)
'corsair loses head' is the wordplay.
'corsair' becomes 'pirate' (I've seen this before).
'loses head' means to remove the first letter.
'pirate' with its initial letter taken off is 'IRATE'.
(Other definitions for irate that I've seen before include "having got in wax" , "will be up in arms" , "Wild" , "Angry and incensed" , "Fuming" .)