Instrument

1. A device used to produce music. What instrument do you play in the band?
2. A measuring or displaying device. That instrument measures voltage.
3. A tool, implement used for manipulation or measurement. The dentist set down his tray of instruments.
4. (law) A legal document, such as a contract, deed, trust, mortgage, or will. Negotiable instruments are the foundation of the money markets.
5. A person used as a mere tool for achieving a goal. Our lawyer was the instrument for success in our legal battles.