in·stru·ment / ˈinstrəmənt/ • n. 1. a tool or implement, esp. one for delicate or scientific work: a surgical instrument writing instruments. ∎  a thing used in pursuing an aim or policy; a means: drama as an instrument of learning. ∎  a person who is exploited or made use of: he was a mere instrument acting under coercion.2. a measuring device used to gauge the level, position, speed, etc., of something, esp. a motor vehicle or aircraft.3. (also musical instrument) an object or device for producing musical sounds: a percussion instrument.4. a formal document, esp. a legal one: execution involves signature and unconditional delivery of the instrument.• v. [tr.] equip (something) with measuring instruments.

instrument tool, implement XIII (earliest of a musical instrument); something used by an agent; means XIV; legal document XV. — (O)F. — L. instrūmentum, f. instruere; see prec. and -MENT.
So instrumental serving as instrument or means XIV; of music composed for instruments XVI (whence instrumentalist XIX); (gram.) XIX. instrumentation composition of music for instruments XIX. instrumentality XVII.

instrument To add code to software, or devices to hardware, in order to monitor (and sometimes control) operation of a system or component while under test or analysis. The code or devices so used are called instrumentation. Instrumenting code may, for example, write to a report file the before and after values of a variable together with a source reference to the code each time the variable is referenced. Some software environments provide tools to automatically add (and remove) the instrumentation and to analyze report files or screen-directed output.

INSTRUMENT

A formal or legal written document; a document in writing, such as a deed, lease, bond, contract, or will. A writing that serves as evidence of an individual's right to collect money, such as a check.