Interrex | Webster's Dictionary of the English Language

interrex
inter-rex, rēgis, m., I one who held the regal office between the death of one king and the election...

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.
interrex
inter-rēx rēgis, m a temporary king, viceroy, regent, interrex, L.—In the republic, a temporary chi...

An Elementary Latin Dictionary