The most common and most likely answer to this crossword clue is the 7 letter word SOLOIST
I've seen this crossword clue in The Daily Telegraph
S
O
L
O
I
S
T
More clues leading to the result SOLOIST
- Stool is specially made for piano player, perhaps
- Oscar is lost at sea, he's all alone
- . Lane close to Kent bores drunk musician
- Loner? Perhaps Napoleon I’s tendency at first
- Therefore catalogue must include old performer
- One who performs thus is included in great deal
- Only one playing thus is in group
- He won’t play with anybody
- One who doesn't play with anybody else
- Lone musician very confused about Scarlatti’s finale
Buddy explains!

The straight part
We know that "person unaccompanied" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case person unaccompanied = soloist.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 SOLOIST mean?
SOLOIST noun- A person who performs a solo.