The most common and most likely answer to this crossword clue is the 8 letter word DROLLEST
I've seen this crossword clue in The Daily Telegraph
D
R
O
L
L
E
S
T
More clues leading to the result DROLLEST
Buddy explains!

The straight part
We know that "Most amusing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most amusing = drollest.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 DROLLEST mean?
DROLLEST adjective- Oddly humorous; whimsical, amusing in a quaint way; waggish.