The creator of this medium, WardCunningham coined the term "wiki wiki web" to a) avoid calling it just "quick web" and b) obtain the WWW acronym. Since then, "wiki wiki web" has degenerated to just "wiki".
On the other hand, wiki wiki, is as you see, WikiWiki. Since "Wiki" is shorter to type, the Wiki:WikiWay applied to its name itself (combined with OccamsRazor) naturally lead to the abreviation "Wiki" in many combinations of WikiName''s. :-)