The Collaborative International Dictionary
Cestuy que trust
Cestuy \Ces"tuy\ or ||Cestui \Ces"tui\, pron. [Norm. F.] (Law) He; the one.
Cestuy que trust[norm. F.], a person who has the equitable
and beneficial interest in property, the legal interest in
which is vested in a trustee.
--Wharton.
Cestuy que use[Norm. F.], a person for whose use land, etc., is granted to another.
Wiktionary
cestuy que trust
n. (context legal English) One who has the equitable and beneficial interest in property, the legal interest in which is vested in a trustee.