The most common and most likely answer to this crossword clue is the 4 letter word BOOK
I've seen this crossword clue in Financial Times
B
O
O
K
More clues leading to the result BOOK
- Volume runs from stream
- Shocker with Kafka's first novel
- Personal problem? Fine to show reserve
- Reserve men on board enjoying quoits?
- A piece of 4 or 19 youth’s not completed satisfactorily
- Quick work to follow 3 20 22!
- Show yellow card to reserve
- Reserve bank’s head allowed to keep nothing
- One’s bound to show reserve
- Disapprove of entrance to Kenyan reserve
Buddy explains!

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 BOOK mean?
BOOK noun- A collection of sheets of paper bound together to hinge at one edge, containing printed or written material, pictures, etc.
- A long work fit for publication, typically prose, such as a novel or textbook, and typically published as such a bound collection of sheets, but now sometimes electronically as an e-book.
- A major division of a long work.
- A record of betting (from the use of a notebook to record what each person has bet).
- A convenient collection, in a form resembling a book, of small paper items for individual use.
- The script of a musical or opera.
- (usually in the plural) Records of the accounts of a business.
- A book award, a recognition for receiving the highest grade in a class (traditionally an actual book, but recently more likely a letter or certificate acknowledging the achievement).
- (whist) Six tricks taken by one side.
- Four of a kind
- A document, held by the referee, of the incidents happened in the game.
- (by extension) A list of all players who have been booked (received a warning) in a game.
- The twenty-sixth Lenormand card.
- Any source of instruction.
- To reserve (something) for future use.
- To write down, to register or record in a book or as in a book.
- (law enforcement) To record the name and other details of a suspected offender and the offence for later judicial action.
- To issue with a caution, usually a yellow card, or a red card if a yellow card has already been issued.
- To travel very fast.
- To record bets as bookmaker.
- (law student slang) To receive the highest grade in a class.
- To leave.
- (with person as subject) To cook (something) in an oven.
- (with baked thing as subject) To be cooked in an oven.
- To be warmed to drying and hardening.
- To dry by heat.
- To be hot.
- To cause to be hot.
- To smoke marijuana.
- To harden by cold.
- To fix (lighting, reflections, etc.) as part of the texture of an object to improve rendering performance.
- (with "in" or "into") To incorporate into something greater.