Cestui que is a shortened version of "cestui a que use le feoffment fuit fait", lit. 'the person for whose use/benefit the feoffment was made'; in modern terms, it corresponds to a beneficiary. It is a Law French phrase of medieval English invention, which appears in the legal phrases cestui que trust, cestui que use, or cestui que vie. In contemporary English the phrase is also commonly pronounced "setty-kay" or "sesty-kay". According to Roebuck, Cestui que use is pronounced. Cestui que use and cestui que trust are often interchangeable. In some medieval documents it is seen as cestui a que. In formal legal discourse it is often used to refer to the relative novelty of a trust itself, before that English term became acceptable.

Law French is an archaic language originally based on Anglo-Norman, but increasingly influenced by Parisian French and, later, English. It was used in the law courts of England, since the 13th century. Its use continued for several centuries in the courts of England and Wales and Ireland. Although Law French as a narrative legal language is obsolete, many individual Law French terms continue to be used by lawyers and judges in common law jurisdictions.