Definition: of or pertaining to the third day, the day before yesterdayThe Latin nunc dies tertius est means â€˜now it is the third dayâ€™ and the phrase nudius tertius literally means â€˜today, thirdâ€™. Most of us live the same lives, with some little adjustments. Some are married, others are single. Some are married to men, others to women. Some work from the office, others from home. Some are vegetarian others cannot survive a day without meat.