...about to go past parliamentarian (9)
I believe the answer is:
roundhead
'past parliamentarian' is the definition.
'roundhead' can be an answer for 'parliamentarian' (I've seen this before). I am unsure of the 'past' bit.
'about to go' is the wordplay.
'about' becomes 'round' (round can mean around or about).
'to go' becomes 'head' (I've seen this in another clue).
'round'+'head'='ROUNDHEAD'
Can you help me to learn more?
(Other definitions for roundhead that I've seen before include "Parliamentarian (hist.)" , "Supporter of Parliament during the English Civil Wars" , "antimonarchist" , "Old soldier" , "Cavalier's foe" .)