interregnum
noun[L. inter and regnum, rule or reign.]
The time in which a throne is vacant, between the death or abdication of a king and the accession of his successor. An interregnum, in strictness, can happen only in governments where the king is elective; for in hereditary kingdoms, the reign of the successor commences at the moment of his predecessor's death or demise. The word however is used with more latitude.