A sonata is a “composition for one or more solo instruments, one of which is usually a keyboard instrument, usually consisting of three or four independent movements varying in key, mood, and tempo,” according to The Free Dictionary.
The word came into English in the 1690s, according to the Online Etymology Dictionary, and it was taken from “Italian sonata, ‘piece of instrumental music,’ literally ‘sounded’ (i.e. ‘played on an instrument,’ as opposed to cantata ‘sung’).”
“The term took on increasing importance in the Classical period, and by the early 19th century the word came to represent a principle of composing large scale works,” according to Wikipedia.
Ludwig van Beethoven's manuscript sketch for Piano Sonata No. 28, Movement IV
Photo courtesy of Wikipedia