The most common and most likely answer to this crossword clue is the 13 letter word CONTRABASSOON
C
O
N
T
R
A
B
A
S
S
O
O
N
Buddy explains!
The straight part
We know that "Instrument" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case instrument = contrabassoon.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 CONTRABASSOON mean?
CONTRABASSOON noun- A larger version of the bassoon sounding one octave lower, having a technique similar to the bassoon but offers more resistance in every way.