Smear most of book cover's contents (4)
I believe the answer is:
blur
'smear' is the definition.
(synonyms)
'most of book cover's contents' is the wordplay.
'most of' means to remove the last letter.
'book' becomes 'blue book' (blue book is a kind of book).
'cover's contents' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'blue' with its last letter removed is 'blu'.
'blu'+'r'='BLUR'
Can you help me to learn more?
(Other definitions for blur that I've seen before include "Out-of-focus image" , "Indistinct mark" , "Hazy or indistinct representation" , "Befog" , "Group - smudge" .)