Except having left serf (5)
I believe the answer is:
slave
'serf' is the definition.
(I've seen this in another clue)
'except having left' is the wordplay.
'except' becomes 'save' (I've seen this before).
'having' indicates putting letters inside.
'left' becomes 'l' (common abbreviation).
'save' placed around 'l' is 'SLAVE'.
(Other definitions for slave that I've seen before include "Person owned by another" , "Person owned for work" , "Person in bondage" , "Drudge" , "Work excessively hard" .)