term:

Instrument

instrument n

1 : a means or implement by which something is achieved, performed, or furthered [an of crime]
2 : a document (as a deed, will, bond, note, certificate of deposit, insurance policy, warrant, or writ) evidencing rights or duties esp. of one party to another under the law [no person is liable on an unless his signature appears thereon "Uniform Commercial Code"] [an indictment is a form of charging ]
;specif
: negotiable instrument

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.