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.-a contrivance or implement, by which musical sounds are produced; as, a musical instrument.-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.-one who, or that which, is made a means, or is caused to serve a purpose; a medium, means, or agent.-to perform upon an instrument; to prepare for an instrument; as, a sonata instrumented for orchestra.