The most common and most likely answer to this crossword clue is the 3 plus 6 plus 6 letter word OUR MUTUAL FRIEND
I've seen this crossword clue in The Guardian
O
U
R
M
U
T
U
A
L
F
R
I
E
N
D
More clues leading to the result OUR MUTUAL FRIEND
- Work in China shared between us?
- Novel, one we both know well
- Work in China for US?
- Victorian novel in which Spooner solicits orange healer?
- Story from someone we both know and like?
- Book distressing a dutiful mourner
- Novel, one that’s familiar to you and Everyman
- Different future in a rum old Victorian tale
- Book my pal and yours
- Novel rumour, futile and garbled
Buddy explains!
The straight part
We know that "Book " is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case book = our mutual friend.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.