What is the origin of the word pikey?

Answer 1

The definition loosely refers to a large portion of the underclass of a country or a person in any social class who lives "on the cheap." The term is also considered to have a racist meaning, and it is considered derogatory and offensive. It's also frequently used as an adjective but also sometimes used as a verb, synonymous with "steal." This term is used in the fringes of Greater London and particularly in the region of West London where large numbers of gypsies have settled over the decades. It is used as a descriptions of those people and their class. It is similar to the American term "white trash."

Answer 2

It's a pejorative slang term in use since the 16th century. The Oxford Dictionary of Slang would be of great use to you.