instrument (n.)

mid-15c., "supplementary payment, amount needed to complete repayment," from Late Latin implementem "a filling up" (as with provisions), from Latin implere "to fill, fill up, make full; fatten; fulfill, satisfy," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + plere "to fill" (from PIE root *pele- (1) "to fill").

The sense of "workman's tool, utensil of a trade, things necessary to do work" is by 1530s. The underlying connection of the senses is "whatever may supply a want, that which fills up a need." Related: Implemental; implements.

An implement is whatever may supply a want or a requisite to an end ; it is always regarded in reference to its particular use ; as, agricultural implements ; implements of war. An instrument is anything which is employed in doing work or producing a certain result ; as, surgical, mathematical, musical instruments. [Century Dictionary]

late 14c., "of the nature of an instrument, serving as a means to an end," from Old French instrumental, from Medieval Latin *instrumentalis, from Latin instrumentum "a tool, apparatus" (see instrument (n.)). Meaning "serviceable, useful" is from c. 1600. Of music, c. 1500; noun meaning "musical composition for instruments only" is attested by 1940. Related: Instrumentally; instrumentality.