Demise, in its original meaning, is an Anglo-Norman legal term (from French démettre, from Latin dimittere, to send away) for the transfer of an estate, especially by lease. The word has an operative effect in a lease, implying a covenant "for quiet enjoyment."
The phrase "demise of the Crown" is used in English law to signify the immediate transfer of the sovereignty, with all its attributes and prerogatives, to the successor without any interregnum in accordance with the maxim "the Crown never dies." At common law the death of the sovereign eo facto dissolved Parliament, but this was abolished by the Representation of the People Act 1867. Similarly the common law doctrine that all offices held under the Crown determined [were terminated?] at its demise has been reversed by the Demise of the Crown Act 1901.
Origin of word "demise"
Through euphemism, "(a person's) demise" is often used as a stilted term for a person's death.
- Burrill, Alexander Mansfield (1850). A new law dictionary and glossary: containing full definitions of the principal terms of the common and civil law. Part 1. New York: John S. Voorhies. p. 361.