The most common and most likely answer to this crossword clue is the 10 letter word PIANOFORTE
I've seen this crossword clue in The Daily Telegraph
P
I
A
N
O
F
O
R
T
E
More clues leading to the result PIANOFORTE
Buddy explains!

The straight part
We know that "grand, possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grand, possibly = pianoforte.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 PIANOFORTE mean?
PIANOFORTE noun- A piano.