Listen, Pesach doesn't mean Passover. Passover means Passover and Pesach derives from the word "pe" for mouth and "sach," which means to converse.
Pesach, thus means the mouth that speaks. This is emblematic of the holiday in general, as it is a festival of freedom and only the free have the ability to speak freely from the mouth.
EDIT: Okay, I suppose I should issue you some sources, right? You can find information about this on any of these: Hagshama.org, Rabbi Mordechai Gafni also writes about this here, as well as in a piece by the OU that can be found here. Pesach is noted in m-w.com as first appearing in 1613, and Passover is dated to 1530. Thanks for suggesting I post some sources, David!