Subversion headed off in issue of book (7)
I believe the answer is:
edition
'book' is the definition.
'subversion headed off in issue of' is the wordplay.
I cannot really understand how this works, but
'of' could be 'o' and 'o' is found within the answer.
'in' is found in the answer.
The remaining letters 'edit' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for edition that I've seen before include "Copy - I tied on (anag)" , "Total number of copies issued (of book)" , "Volume" , "copy of work" , "One version of a published text" .)