The use of something even though not owning it.
The old word for a trust beneficiary was cestui que use.
A creation of Roman Law, a use was the precursor to modern trust law and in medieval common law, it was the word used to describe what today, lawyers would call a trust.
Bouvier defines a trust using these words:
"A trust is merely what a use was before the statute of uses. The words use and trust are frequently used indifferently."
The structure of a use gradually attracted the attention of the British royalty in their never-ending quest to arrest any activity that tended to reduce the obligations of citizens to the Crown. With the use, an owner was separated from the person using land which made taxation and other politically expedient policies difficult, as the owner's identity was not readily apparent.
To rectify this, a statute which became known as the Statute of Uses was passed in 1535 which looked over this anomaly by treating the cestui que use as the owner in the eyes of the law.
But lawyers and time, it seems, are formidable foes and before long, a new legal creature emerged (trusts) which, many legal historians note, were simply uses wearing different terminology apparel - effectively circumventing what the Statute of Uses.
There is some debate as to the origin of the word.
Many believe it comes form the Latin word opus as in ad opus or "on behalf of another". Thus, in Equity (Cambridge: University Press, 1949, at page 25), author F. Maitland describes a use as "land ... permanently held by one man to the use (ad opus) of another".