The most common and most likely answer to this crossword clue is the 4 letter word BETS
I've seen this crossword clue in Independent
B
E
T
S
More clues leading to the result BETS
Buddy explains!
The straight part
We know that "Contents of book?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case contents of book? = bets.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BETS mean?
BETS noun- A wager, an agreement between two parties that a stake (usually money) will be paid by the loser to the winner (the winner being the one who correctly forecast the outcome of an event).
- A degree of certainty.
- To stake or pledge upon the outcome of an event; to wager.
- To be sure of something; to be able to count on something.
- To place money into the pot in order to require others do the same, usually only used for the first person to place money in the pot on each round.