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1767, from Italian, from piano e forte "soft and loud," in full, gravicembalo col piano e forte "harpsichord with soft and loud" (c.1710), said to have been so named by inventor Bartolomeo Cristofori (1655-1731) of Padua because the ability via dampers to vary the tone is one of the main changes from the harpsichord. Italian piano (adj.) ultimately is from Latin planus "flat, smooth, even," later "soft" (see plane (n.1)).
The full name of the piano, the common musical instrument with a board of black and white keys, eighty-eight in all. The keys operate hammers that strike wires. Pianoforte is Italian for “soft-loud”; it received this name because its level of loudness depends on how hard the player strikes the keys.