Interregnum \In`ter*reg"num\, n.; pl. {Interregnums}. [L., fr. inter between + regnum dominion, reign. See {Reign}, and cf. {Interreign}.] 1. The time during which a throne is vacant between the death or abdication of a sovereign and the accession of his successor. 2. Any period during which, for any cause, the executive branch of a government is suspended or interrupted.