Victoria, after New Act, rings about book size (6)
I believe the answer is:
octavo
'book size' is the definition.
(I've seen this in another clue)
'victoria after new act rings' is the wordplay.
I cannot really understand how this works, but
an anagram of 'act' is 'cta' which is within the answer.
The remaining letters 'ovo' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'about' acts as a link.
Can you help me to learn more?
(Other definitions for octavo that I've seen before include "Common book size" , "An eight-leaved book or page" , "Size of book page" , "Size of a book, pages are made by folding a sheet of paper three times to form eight leaves (6)" .)