The most common and most likely answer to this crossword clue is the 9 plus 1 plus 2 letter word TRENCHANT - DD
I've seen this crossword clue in The Times
T
R
E
N
C
H
A
N
T
-
D
D
Buddy explains!
The straight part
We know that "Sharp/blunt" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sharp/blunt = trenchant - dd.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.