means A keyboard instrument that produces sound when felt-covered hammers strike metal strings, capable of playing both softly and loudly depending on how hard the keys are pressed.

from Short for the Italian 'pianoforte,' which smashes together 'piano' (soft) and 'forte' (loud) — a name that bragged about the instrument's revolutionary trick: unlike the harpsichord, it could play quietly OR loudly depending on your touch. 'Piano' itself comes from Latin 'planus' (flat, smooth, level), a cousin of 'plain' and 'plane,' which drifted in Italian toward the sense of 'gentle' or 'soft.' Over time everyone got lazy and dropped the 'forte,' leaving the instrument named only for its quiet half — fitting, given the essence's accusation.