The most common and most likely answer to this crossword clue is the 9 letter word MAINLINED
I've seen this crossword clue in The Daily Telegraph
M
A
I
N
L
I
N
E
D
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 MAINLINED mean?
MAINLINED verb- To inject (a drug) directly into a vein.
- To integrate (code, etc.) into the main repository for a software project, rather than separate forks.