The most common and most likely answer to this crossword clue is the 9 letter word PASSAGING
I've seen this crossword clue in The Daily Telegraph
P
A
S
S
A
G
I
N
G
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 PASSAGING mean?
PASSAGING verb- To pass something, such as a pathogen or stem cell, through a host or medium
- To make a passage, especially by sea; to cross
- To execute a passage movement