Administrator: A person appointed by the court to manage the assets and liabilities of an intestate decedent.
Beneficiary: A person to whom another is in a fiduciary relation, whether the relation is one of agency, guardianship, or trust; especially, a person for whose benefit property is held in trust
Decedent: A dead person, especially one who has died recently.
Devise: The act of giving property by will. Although this term traditionally referred to gifts of real property—and in British usage the term is still confined to real property—in American usage the term has been considerably broadened.
Executor: A person named by a testator to carry out the provisions in the testator's will.
Intestate: Someone who has died without a valid will.
Legacy: A gift by will, esp. of personal property and often of money.
Probate: The judicial procedure by which a testamentary document is established to be a valid will; the proving of a will to the satisfaction of the court.
Testator/testatrix: A person who has made a will; especially, a person who dies leaving a will.
Trust: The right, enforceable solely in equity, to the beneficial enjoyment of property to which another person holds the legal title; a property interest held by one person (the trustee) at the request of another (the settlor) for the benefit of a third party (the beneficiary).
Will: The legal expression of an individual's wishes about the disposition of his or her property after death; especially, a document by which a person directs his or her estate to be distributed upon death .
All definitions come from Black’s Law Dictionary (11th ed. 2019).