Early 19th century (originally denoting a member of the Irish constabulary): from the name of Sir Robert Peel, Sir Robert.

• bob from Late Middle English:

  Short words are often the hardest to pin down, and this is the case with bob, which has many uses. Some imply ‘short’; for example, the hairstyle, which became fashionable in the 1920s. Before that people had used bob for a horse's docked tail, a short bunch of hair or curls, and a short wig, and the bob in bobcat (late 19th century), bobsleigh (mid 19th century), and bobtail (mid 16th century) also means ‘short’.

  Another set of uses involves a quick, short movement. People and things bob up and down, and boxers bob and weave. The British bob, ‘a shilling’, dating from the late 18th century, does not appear to be related to any of these, and its origin remains a mystery.

  Bob's your uncle, used to draw attention to the ease with which something can be done, is from the pet form of the name Robert. The Robert in question may have been Lord Salisbury, who in 1887 gave the important post of Chief Secretary for Ireland to his nephew, Arthur Balfour, who was only 39 at the time. The problem with this suggestion is that the earliest recorded examples do not appear until the 1930s, around 50 years after the incident in question. However, we do know that the British bobby comes from Sir Robert Peel, British Home Secretary from 1828–30, who established the Metropolitan Police. The old-fashioned term peelers for policemen also comes from his name.