The most common and most likely answer to this crossword clue is the 8 letter word PANPIPES
I've seen this crossword clue in The Times
P
A
N
P
I
P
E
S
Buddy explains!
The straight part
We know that "another instrument one blows across?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case another instrument one blows across? = panpipes.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.