Since the Norman conquests, English law has used many expressions that are often said to be derived from Old French. In fact, during the Middle Ages, a real language, Law French, combining Latin and Anglo-Norman, was used in the courts and by professors until the eighteenth century. The same is true of the expression cestui que trust, still used today to designate the beneficiary of a trust. This expression, that we may consider a symbol of an international legal world before its time, remains enigmatic in many respects. However, by analysing the principle of trust, we can understand the link trust-Equity-use and gain a better understanding of the expression cestui que use, the ancestor of the cestui que trust. The etymology of the locution cestui que trust allows us to assume, but not to affirm, that its origins lie in Saxon, Latin and Anglo-Norman.
Anne-Sophie Milard (Mon,) studied this question.