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1. A tool or implement used to do or facilitate work, especially a small precision tool used by a professional: sterilized the scalpel and other surgical instruments.
2. A device for recording, measuring, or controlling, especially such a device functioning as part of a control system.
3. Music A device designed to enable a person to make musical sounds, as by blowing into it, striking it, depressing the keys on a keyboard, or plucking, strumming, or running a bow over strings.
4. A means by which something is done; an agency: "The gods are just, and of our pleasant vices / Make instruments to plague us" (Shakespeare).
5. One used by another to accomplish a purpose; a dupe.
6. A legal document, especially one that represents a right of payment or conveys an interest, such as a check, promissory note, deed, or will.
tr.v. (-mĕnt′) in·stru·ment·ed, in·stru·ment·ing, in·stru·ments
1. To provide or equip with instruments.
2. Music To compose or arrange for performance.
[Middle English, from Old French, from Latin īnstrūmentum, tool, implement, from īnstruere, to prepare; see instruct.]