(Lat. onus probandi.) In the law of evldence. The neces-slty or duty of affirmatively provlng a fact or facts in dispute on an issue raised between the parties In a cause, willett v. Rich, 142 Mass. 356, 7 N. E. 776, 56 Am. Rep. 684; wilder v. Cowles, 100 Mass. 490; People v. McCann, 16 N. Y. 58, 69 Am. Dec. 642