From http://textbook.wikipedia.org/wiki/Wikibooks:Staff_lounge
I know that the name "Wikibooks" was thought of and promoted by me, but that was before we really knew where we wanted to go with this project (become an educational resource). The word "Wikipedia" is obviously the name of an encyclopedia and the word "Wiktionary" is obviously the name of a dictionary. But "Wikibooks" doesn't bring anything specific in mind. So what does everybody think of the name "Wikiuniversity"? Our aim is to create a huge educational resource and I think that such a name would be more fitting to such an endeavor.
-- Daniel Mayer (aka mav)