Obscure promotion, dismissing second book (4)
I believe the answer is:
blur
'obscure' is the definition.
(synonyms)
'promotion dismissing second book' is the wordplay.
I cannot quite understand how this works, but
'second' could be 'b' (B can mean second eg B-side) and 'b' is located in the answer.
The remaining letters 'lur' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for blur that I've seen before include "Group - smudge" , "Indistinct mark" , "Muddle" , "Become unclear" , "Make or become indistinct" .)