inter-regnum (noun N) :
* The time between the death of one king and the election of another, an interregnum: populus flagitare regem non destitit; cum . . . illi principes novam interregni ineundi rationem excogitaverunt,Cic. Rep. 2, 12, 23: id ab re, quod nunc quoque tenet nomen, interregnum appellatum,Liv. 1, 17.
* Transf., under the republic, the time between the death or departure of the consuls and the choice of new ones: res ad interregnum venit,Cic. Att. 9, 9, 3: rem adduci ad interregnum,id. ib. 7, 9, 2: per interregnum renovare auspicia,Liv. 5, 31, 7: interregnum inire, to become interrex, id. 3, 8.

s. TLL