(Law) A solemn, authentic instrument in writing, by which a person declares his will as to disposal of his estate and effects after his death. Note: This is otherwise called a will, and sometimes a last will and testament. A testament, to be valid, must be made by a person of sound mind; and it must be executed and published in due form of law. A man, in certain cases, may make a valid will by word of mouth only. See Nuncupative will, under Nuncupative.