Webster's Revised Unabridged Dictionary · 1913

Cestuy

Cestuy , pronoun

[Norm. French]

(Law) He; the one.
Collocations (2)
Cestuy que trust , 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 , a person for whose use land, etc., is granted to another.

Also: Cestui