Can good boy put across whopper ultimately? (6)
I believe the answer is:
prison
'can' is the definition.
(The Can is slang for prison)
'good boy put across whopper ultimately?' is the wordplay.
'good' becomes 'pi' (old-fashioned term for pious).
'boy put' becomes 'son' (I can't explain this - if you can you should give a lot more credence to this answer).
'across' means one lot of letters goes inside another.
'ultimately?' says to take the final letters (I've seen 'ultimately' mean this).
The final letter of 'whopper' is 'r'.
'pi'+'son'='pison'
'pison' going around 'r' is 'PRISON'.
Can you help me to learn more?
(Other definitions for prison that I've seen before include "Slammer" , "cage" , "Correctional institution" , "punishment" , "Cooler" .)