A popular English nursery rhyme,
Hickory Dickory Dock,
the mouse ran up the clock
the clock struck one,
the mouse ran down
Hickory Dickory Dock.
One theory of the origin of the phrase 'Hickory Dickory Dock' is that it is from the counting system used by shepherds in the North of England, the Yan Tan Tethera. In the Westmoreland the numbers eight, nine, and ten were given as Hevera, Devera, and Dick; a northern accent might also explain how the words 'one' and 'down' could be considered to rhyme.
Another theory is that Hickory Dickory Dock is a play on the name Richard, which was commonly shortened not only to Rick, but also to Hick and Dick. The common use of rhyming nicknames and a multitude of diminitives might account for Hickory and Dickory, but do not explain Dock.
Of course, we do not know what the original version might have been. The rhyme first appeared in the written record in Tommy Thumb's Pretty Song Book, which was published in London around about 1744. This version used the line: 'Hickere, Dickere Dock'. The next appearance was in Mother Goose's Melody (c. 1765), which used 'Dickery, Dickery Dock'. Other regional variations include the Scottish "Zoccotty dicotty dock", (recorded from 1810), the Shropshire "Ickity pickety pock" (1883), and the Kirkwall "Rickety rickety rock" (1911).
Roud Folk Song Index #6489