An instrument that shows direction without knowing the destination. A compass orients; it does not choose.
Old French compas (circle, measure, pair of dividers), from compasser (to measure out, divide equally), from Vulgar Latin *compassare: com- (together) + passus (a step, pace). Literally "to pace out together". The magnetic navigation sense arrives in English in the 14th century, the drawing-instrument sense earlier; both keep the idea of stepping out a measured circle.
The music player — the sovereign, local-first one. The root is apt beyond the navigation reading: a compass paces something OUT, step by measured step, which is what a library is. And a compass points; it does not decide where you go.