The most common and most likely answer to this crossword clue is the 11 letter word SYNTHESISER
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More clues leading to the result SYNTHESISER
Buddy explains!

The straight part
We know that "an electronic instrument" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an electronic instrument = synthesiser.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 SYNTHESISER mean?
SYNTHESISER noun- An electronic instrument that creates its sounds with electronics and has a keyboard.
- An electronic instrument module that creates its sounds with electronics and does not have any keyboard.
- An electronic circuit that generates an electronic signal oscillation with accurate timing from a reference oscillator.
- An electronic device that generates electronic signal patterns to test an electronic circuit.