The most common and most likely answer to this crossword clue is the 9 letter word RADICALLY
R
A
D
I
C
A
L
L
Y
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 RADICALLY mean?
RADICALLY adverb- In a radical manner; fundamentally; very.
- At the root.