The most common and most likely answer to this crossword clue is the 8 letter word READIEST
I've seen this crossword clue in The Times
R
E
A
D
I
E
S
T
Buddy explains!
The straight part
We know that "Most willing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most willing = readiest.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 READIEST mean?
READIEST adjective- Prepared for immediate action or use.
- Inclined; apt to happen.
- Liable at any moment.
- Not slow or hesitating; quick in action or perception of any kind.
- Offering itself at once; at hand; opportune; convenient.