Instrument, n.
Etymology: [F. instrument, L. instrumentum. See Instruct.]
1. That by means of which any work is performed, or result is effected; a tool; a utensil; an implement; as, the instruments of a mechanic; astronomical instruments. All the lofty instruments of war. Shak.
2. A contrivance or implement, by which musical sounds are produced; as, a musical instrument. Praise him with stringed instruments and organs. Ps. cl. 4. But signs when songs and instruments he hears. Dryden.
3. (Law)
A writing, as the means of giving formal expression to some act; a writing expressive of some act, contract, process, as a deed, contract, writ, etc. Burrill.
2 more senses
4. One who, or that which, is made a means, or is caused to serve a purpose; a medium, means, or agent. Or useful serving man and instrument, To any sovereign state. Shak. The bold are but the instruments of the wise. Dryden.
Syn. -- Tool; implement; utensil; machine; apparatus; channel; agent.
1 other Webster entry under this spelling
Instrument, v. t.
To perform upon an instrument; to prepare for an instrument; as, a sonata instrumented for orchestra.
Shades of meaning
Fernald has no entry of its own for instrument; he lists it under agent, record, tool.
Where he writes about it:
But in common usage, especially in business, an agent is not the prime actor, but only an instrument or factor, acting under orders or instructions. — from agent
An instrument is anything through which power is applied and a result produced; in general usage, the word is of considerably wider meaning than tool; as, a piano is a musical instrument. — from tool
Instrument is the word usually applied to tools used in scientific pursuits; as, we speak of a surgeon's or an optician's instruments. — from tool
A machine in the most general sense is any mechanical instrument for the conversion of motion; in this sense a lever is a machine; but in more commonly accepted usage a machine is distinguished from a tool by its complexity, and by the combination and coordination of powers and movements for the production of a result. — from tool
Implement is for the most part and utensil is altogether restricted to the literal sense; instrument, machine, and tool have figurative use, instrument being used largely in a good, tool always in a bad sense; machine inclines to the unfavorable sense, as implying that human agents are made mechanically subservient to some controlling will; as, an instrument of Providence; the tool of a tyrant; a political machine. — from tool