I sloped off to plunder (7)
I believe the answer is:
despoil
'to plunder' is the definition.
('despoil' can be a synonym of 'plunder')
'i sloped off' is the wordplay.
'off' indicates anagramming the letters.
'i'+'sloped'='isloped'
'isloped' is an anagram of 'DESPOIL'.
(Other definitions for despoil that I've seen before include "Plunder completely" , "Plunder, devastate" , "Plunder (a place)" , "Plunder, rob" , "Ravage" .)