It's Austen on one side, latterly, or the Queen if you turn it over (6)
I believe the answer is:
tenner
'the queen if you turn it over' is the definition.
I can't tell whether this definition defines the answer.
'it's austen on one side latterly' is the wordplay.
'on one side' indicates taking half (one side of the word).
'latterly' becomes 'ner' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'austen' cut in half is 'ten'.
'ten'+'ner'='TENNER'
'or' is the link.
Can you help me to learn more?
(Other definitions for tenner that I've seen before include "Heard bell" , "Note - sounds like singer" , "A spot of money" , "little money" , "UK banknote" .)