Previous head of state oppressed by class (6)
I believe the answer is:
former
'previous' is the definition.
(I know that previous can be written as former)
'oppressed by class' is the wordplay.
'oppressed' becomes 'er' (I can't explain this - if you can you should believe this answer much more).
'by' says to put letters next to each other.
'class' becomes 'form class' (synonyms).
'er' after 'form' is 'FORMER'.
'head of state' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for former that I've seen before include "First-mentioned" , "long ago" , "late" , "Of an earlier period, or mentioned before another" , "Old < prior < departed" .)