Some concoct a vocabulary for a size of paper (6)
I believe the answer is:
octavo
'size of paper' is the definition.
'octavo' can be an answer for 'size' (octavo is a kind of size). I'm not sure about the 'of paper' bit.
'some concoct a vocabulary' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'OCTAVO' is hidden in the letters of 'concoct a vocabulary'.
'for a' is the link.
Can you help me to learn more?
(Other definitions for octavo that I've seen before include "An eight-leaved book or page" , "Size of book page" , "Common book size" , "Size of a book, pages are made by folding a sheet of paper three times to form eight leaves (6)" .)