A tool; a mechanism for scientific or musical purposes.
A legal writing.
Bruce picked up the instrument. – Counsel for the Defense by Leroy Scott
With an astonished exclamation, Garrity put the instrument down. – Lefty Locke Pitcher-Manager by Burt L. Standish
First he kept it to himself as a future instrument of profit. – Checkmate by Joseph Sheridan Le Fanu