Openings for blackmail – one’s agreed record of gambling (4)
I believe the answer is:
book
'record of gambling' is the definition.
'book' can be an answer for 'record' (synonyms). I'm not certain of the 'of gambling' bit.
'openings for blackmail one's agreed' is the wordplay.
'openings for' indicates taking the first letters (the letters which open the words).
'agreed' becomes 'ok' (eg when responding to an offer).
The initial letters of 'blackmail ones' is 'bo'.
'bo'+'ok'='BOOK'
Can you help me to learn more?
(Other definitions for book that I've seen before include "Reading volume" , "an item from the library" , "Take down name of offending player" , "Strict rules" , "See 1 ac" .)