The most common and most likely answer to this crossword clue is the 9 letter word BALALAIKA
I've seen this crossword clue in The Times
B
A
L
A
L
A
I
K
A
More clues leading to the result BALALAIKA
- It's played first of all in dance at a milk bar regularly
- Instrument from a laboratory upset first cosmonaut?
- Back room for scientist with a space traveller's instrument
- An experimental institution came up with space explorer’s instrument
- Instrument dog found under lake
- Graduate left answer as a rumoured instrument from Russia
- It needs pluck to play in triangular formation
- Instrument placing dog in space south of lake
- Music maker beginning to bark in the style of a dog who was out of this world
- Instrument found in Welsh lake by dog
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 = balalaika.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 BALALAIKA mean?
BALALAIKA noun- A plucked stringed instrument with a triangular body, short neck and three strings, of Russian origin.