Demise, in its original meaning, is an Anglo-Norman legal term

Law French

Law French is an archaic language originally based on Old Norman and Anglo-Norman, but increasingly influenced by Parisian French and, later, English. It was used in the law courts of England, beginning with the Norman Conquest by William the Conqueror...

 (from French

French language

French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...

 démettre, from Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 dimittere, to send away) for a transfer of an estate

Estate (law)

An estate is the net worth of a person at any point in time. It is the sum of a person's assets - legal rights, interests and entitlements to property of any kind - less all liabilities at that time. The issue is of special legal significance on a question of bankruptcy and death of the person...

, especially by lease

Lease

A lease is a contractual arrangement calling for the lessee to pay the lessor for use of an asset. A rental agreement is a lease in which the asset is tangible property...

. The word has an operative effect in a lease implying a covenant "for quiet enjoyment".

The phrase "demise of the crown

Demise of the Crown

In relation to the shared monarchy of the Commonwealth realms and other monarchies, the demise of the Crown is the legal term for the end of a reign by a king, queen, or emperor, whether by death or abdication....

" 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

Interregnum

An interregnum is a period of discontinuity or "gap" in a government, organization, or social order...

 in accordance with the maxim "the Crown never dies". At common law

Common law

Common law is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action...

 the death of the sovereign eo facto dissolved Parliament, but this was abolished by the Representation of the People Act 1867, 51. Similarly the common law doctrine that all offices held under the crown determined at its demise has been reversed by the Demise of the Crown Act 1901

Demise of the Crown Act 1901

The Demise of the Crown Act 1901 is an Act of Parliament of the Parliament of the United Kingdom.It provides that the holding of any office under the Crown is not to be affected in any way by the death of the reigning monarch, and that it is not necessary for anyone to be reappointed to a position...

.

Origin of word "demise"

The English word "demise" comes from the Latin word "demissio" (see, e.g., ex demissione

Ex demissione

Ex demissione is Legal Latin meaning "upon the demise" -- where "demise" in used in its sense meaning "lease" or "transfer"....

), which comes from Latin "demittere," which is a compound of de + mittere, meaning "to send from".

Through euphemism

Euphemism

A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

, "(a person's) demise" is often used as a stilted term for a person's death.