Burden left for bumpkin (5)
I believe the answer is:
yokel
'bumpkin' is the definition.
('yokel' can be a synonym of 'bumpkin')
'burden left' is the wordplay.
'burden' becomes 'yoke' (I've seen this before).
'left' becomes 'l' (common abbreviation).
'yoke'+'l'='YOKEL'
'for' acts as a link.
(Other definitions for yokel that I've seen before include "Hayseed" , "Rustic - peasant" , "Unsophisticated rustic" , "Countryman" , "Unsophisticated country person" .)