A priest assembled the buccaneers (7)
I believe the answer is:
pirates
'the buccaneers' is the definition.
('pirate' can be a synonym of 'buccaneer')
'a priest assembled' is the wordplay.
'assembled' indicates an anagram.
'a'+'priest'='apriest'
'apriest' is an anagram of 'PIRATES'.
(Other definitions for pirates that I've seen before include "Copies" , "More than one brigand" , "Robbers at sea" , "Robbers on the high seas" , "Bad sailors" .)