A weighty book, but not to you (4)
I believe the answer is:
tome
'a weighty book' is the definition.
(I've seen this before)
'to you' is the wordplay.
'you' becomes 'me' (I can't justify this - if you can you should give a lot more credence to this answer).
'to'+'me'='TOME'
'but not' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tome that I've seen before include "Large scholarly volume" , "Hefty volume" , "Big book" , "Large heavy book" , "Heavy volume" .)