The immoral or unconscionable use of one person’s power over another in order to effect the other person to compromise something, e.g. a property right. For example, a son who visits an ailing, aging father in poor mental health and influences the father to change his will and leave the entire estate to that son and none to the other siblings.
Law Dictionary – Alternative Legal Definition
In regard to the making of a will and other such matters, undue influence is persuasion carried to the point of overpowering the will, or such a control over the person in question as pre-vents him from acting intelligently, understanding, and voluntarily, and in effect de-stroys his free agency, and constrains him to do what he would not have done if such control had not been exercised. Undue influence consists (1) in the use, by one in whom a confidence .is reposed by another, or who holds a real or apparent au-thority over him, of such confidence or au-thoriry, for the purpose of obtaining an unfair advantage over him; (2) in taking an ufifair advantage of another’s weakness of mind; or (3) in taking a grossly oppressive and unfair advantage of another’s necessities or distress. Civ. Code Dak.