This verse has a rhyming and melodic sound that is easy to transpose into similar sounding words. Thus, there are many different versions from different dialects and different places.

Hickory, dickory, dock, The mouse ran up the clock , is said to be a variation of similar words used by Westmorland shepherds in the English countryside to count their sheep Hevera (8), Devera (9), and Dick (10), numbers that you would also find on a clock.

(The Oxford Dictionary of Nursery Rhymes p. 206).

It is also imagined that when the shepherds came home from a hard days work, they often put their children to sleep by "counting sheep" with the same rhyme. (Patrick Rooney.)

Putting children to sleep at night is a very important part of the day, hearing a parents voice and knowing they are nearby; whatever words come out with a rhythmic tone can be comforting and reassuring.

Although there are many versions, this nursery rhyme almost always uses onomatopoeia to "catch the tongue."

Children often repeat the words they hear their parents say, which could explain some of the silliest variations of this rhymer. Rhyming is fun and can make us laugh for hours with our friends. Some variations:

  "Ziccoty diccotty dock," (Blackwoods' Edinburgh Magazine, 1821)

  "The moose ran up the clock" (northeast Scotland 1881)

  "Ickity, Pickety pock"( Shropshire 1883)

(Counting-Out Rhymes A Dictionary. Edited by Roger D. Abrahams and Lois Rankin. University of Texas Press Austin and London , p.98.)

Hickory, diccory, dock was a simple rhyme used to decide who would be "It" in a children's game.

It is easy to imagine children gathered in a circle and pointing to each child in the direction the hands of the clock moves to decide who is to begin a game both then and as far back as could be remembered.

Written in Blackwood's Magazine (1821). (The Oxford Dictionary of Nursery Rhymes p. 206).  

HICKORY (1), Dickory (2), dock (3) 

The mouse ran up the clock (4); 

The clock struck one (5); 

The mouse was gone (6); 

O (7), U (8), T (9), spells OUT! 

(Lang, Andrew, Ed. The Nursery Rhyme Book, Illus. By L. Leslie Brooke, London , England : Frederick Warne and Co., 1897, p. 176