Mid 19th century: from French, humorous alteration of rocaille.

• rock from Old English:

  The hard rock that makes up much of the earth came into medieval English from Old French rocque, which can be traced back to medieval Latin rocca but no further. The classical Latin word was petra, the source of petrify. People have been caught between a rock and a hard place since the 1920s, first of all in Arizona and California. Also American is on the rocks meaning a drink ‘on ice’, first recorded in 1946, while the slang term for a precious stone is 1920s. In France the modern form of the word, roc developed the form rocaille to describe the decoration using shells and pebbles fashionable in the 18th century. In the 19th century this was changed by French workmen to rococo, originally to mean something old-fashioned, but now used to describe the art of the 18th century. Rock meaning ‘to move to and fro’ is an Old English word. Rock music was originally rock and roll, which is first found in 1951, although a song called ‘Rock and Roll’ came out in 1934. Rock and roll combined black rhythm and blues and white country or ‘hillbilly’ music. Elvis Presley's first single, ‘That's All Right Mama’ and Bill Haley's ‘Rock Around the Clock’, both released in 1954, are often considered the first rock and roll records, but similar-sounding music was produced in the 1930s and 1940s by black performers like Big Joe Turner and Fats Domino.

  If you are off your rocker you are mad or crazy. A rocker here is a curved piece of wood or metal placed under a chair or cradle so that it can rock backwards and forwards. In the early 1960s rockers were also youths who liked rock music, leather clothing, and motorcycles, and were the sworn enemies of the mods (short for modernists), who were noted for their smart appearance, motor scooters, and fondness for soul music.