What is the meaning of undue influence in the context of a testamentary disposition?

A more recent statement of the meaning of undue influence is found in the decision of Cullity J. in Banton v. Banton, 1998 CanLii 14926 (ONSC) at para. 89: A testamentary disposition will not be set aside on the ground of undue influence unless it is established on the balance of probabilities that the influence imposed by some other person on the deceased was so great and overpowering that the document reflects the will of the former and not that of the deceased. In such a case, it does not represent the testamentary wishes of the testator and is no more effective than if he or she simply delegated his will-making power to the other person.