inter-rex (noun M) :
* One who held the regal office between the death of one king and the election of another; a regent, interrex, Liv. 1, 17; 1, 32.
* During the times of the republic, one who held the supreme power from the death or absence of the chief magistrates till the election of new ones: L. Flaccus interrex legem de Sulla tulit,Cic. Agr. 3, 2, 5; id. Leg. 1, 15, 42; id. Dom. 14, 38: prodere,to nominate, appoint,id. Agr. 3, 2, 5: creare,Liv. 5, 31, 8: infestam patribus plebem interreges cum accepissent,id. 7, 21.

s. TLL