The oaf takes plenty out of turn (4)
I believe the answer is:
lout
'the oaf' is the definition.
('lout' can be a synonym of 'oaf')
'takes plenty out of turn' is the wordplay.
'takes plenty' becomes 'lu' (I can't explain this - if you can you should give a lot more credence to this answer).
'out' means one lot of letters goes inside another.
'of' becomes 'o''.
'turn' becomes 't' (abbreviation in Oxford Dictionary of Abbreviations).
'lu' placed around 'o' is 'lou'.
'lou'+'t'='LOUT'
Can you help me to learn more?
(Other definitions for lout that I've seen before include "Ignorant, awkward fellow" , "Lob" , "Yob" , "Antisocial person" , "Dolt - oaf" .)