Around the year 1700, Bartolomeo Cristofori was the Keeper of the Instruments for the Grand Prince of Tuscany. Cristofori was an expert maker of harpsichords, but a drawback to these plucked instruments was the utter lack of dynamics. No matter how hard you hit the key, the volume of the note was exactly the same.
So he set about to make a hammered instrument that could be played at different volumes. He named the result un cimbalo di cipresso di piano e forte (“a keyboard of cypress with soft and loud”), which was abbreviated over time as pianoforte, fortepiano, and finally, piano.