The most common and most likely answer to this crossword clue is the 10 letter word PREEMINENT
P
R
E
E
M
I
N
E
N
T
More clues leading to the result PREEMINENT
Buddy explains!
The straight part
We know that "With the greatest authority" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with the greatest authority = preeminent.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 PREEMINENT mean?
PREEMINENT adjective- Exceeding others in quality or rank; of outstanding excellence, extremely notable or important.