Interregnum \in-tuhr-REG-nuhm\ , noun;
plural: interregnums \-nuhmz\ or interregna \-nuh\
1. The interval between any two reigns; any period when a state is left without a ruler
2. A period of freedom from authority or during which government functions are suspended
2. Any breach of continuity in an order; a lapse or interval in a continuity
This word dates to the 1570's and comes from Latin inter + regnum, which is literally "between-reign."
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Saturday, March 19
Etymologies come from the Oxford English Dictionary and/or Etymonline.com