Latin. By virtue of his office. Powers which come from the office obtained that do not need to be specified because they are necessary for the position held. Many powers are granted and exercised by public officers which are not expressly delegated. A judge, for example, may, ex officio, be a conservator of the peace, and a justice of the peace. pl. Ex officiis. From office; by virtue, or as a consequence, of an office; officially.