Giaour

Adjective that I have no idea how to pronounce

One outside of the Islamic faith; infidel

Since he was born well before Mohammed, Nero was definitely a giaour.

This one harkens back to 1564, and does not come from Latin.  In fact it comes from French, who got it from Italian word giaur, who took it from the Turkish word gâvur, who cribbed it from the Persian gawr, or gabr.