The most common and most likely answer to this crossword clue is the 4 letter word INRO
I
N
R
O
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 INRO mean?
INRO noun- A small decorative box, hung from the sash of a kimono, for holding small objects