means a tool or device used to do precise work, make music, or measure something — and figuratively, the means by which a thing is accomplished.

from From Latin 'instrumentum,' meaning a tool, implement, or equipment — built from 'instruere,' 'to build up, arrange, equip,' which itself stacks 'in-' (upon) onto 'struere' (to pile, build). So at its root an instrument is something you've set in order to get a job done — a sibling of 'structure' and 'construct.' English took it through Old French in the medieval period, and over centuries it branched into legal instruments, scientific instruments, and musical ones, all sharing that original sense of a carefully arranged means to an end.