It actually means "soft" in Italian just like "forte" in Italian means loud. Hence, the pianoforte, which I believe was the original name for our modern pianos, means loud-soft because it has loud and soft noise levels. Before the piano, instruments closest in construction to it such as the harpsichord had one level of sound, so the introduction of an instrument that could be played loudly or softly was a dynamic change in the history of music.
