According to WebElements.com, the word "oxygen" comes from the Greek words "oxy" (acid) and "genes" (forming). (As for why oxygen would be named as "acid former", I have no idea - sorry.) You can find more information on the discovery of oxygen by following the above link.
p.s. WebElements references this book as the source for a lot of its historical information. You may be able to find a copy in the library if you're looking for more information.
(published on 10/22/2007)