Mad freebooter relinquishing power (5)
I believe the answer is:
irate
'mad' is the definition.
(thesaurus)
'freebooter relinquishing power' is the wordplay.
'freebooter' becomes 'pirate' (pirate is a kind of freebooter).
'relinquishing' is a deletion indicator.
'power' becomes 'p'.
'pirate' with 'p' removed is 'IRATE'.
(Other definitions for irate that I've seen before include "Annoyed, exasperated" , "Hacked off" , "Infuriated" , "having got in wax" , "I tear away, being annoyed" .)