interregnum - Dictionary definition and meaning for word interregnum
reg stands for king or kingly styles (e.g. in regicide,regalia etc.) so inter regnum = in between two kings(referring to their ruling period).
Inter(Interval)+Regnum (Kingship)-->Interval between kingship, government etc.
inter + regime
he interval between two reigns; any period when a state is left without a ruler
period of no (inter)fering (reg)ime