DISCLAIMER: I read this here today so, unless told otherwise... I'm just going to believe that it's true:
VATICANUS: The Word & its Meaning from which is derived the word Vatican as in Vatican City the Imperial Seat of the Roman Caesars.
VATICAN is derived from two Latin words Vatic-anus.
VATIC- "Characteristic of a prophet; oracular" From Latin: vts, seer -ANUS "The opening at the lower end of the alimentary canal through which solid waste is eliminated from the body" From Latin: nus, ring, anus
VATIC- ANUS = VATICANUS = VATICAN