Overmorrow is a real English word that means the day after tomorrow. It is rare in everyday modern speech, so many native speakers have never heard it, but it has existed in English for centuries.
The word follows an older English pattern. Morrow once commonly meant the next day or morning. Adding over created a word for the day beyond tomorrow. English also has a matching older word, ereyesterday, meaning the day before yesterday, though that is even less common.
Example:
- Common phrasing: We leave the day after tomorrow.
- Less common but correct: We leave overmorrow.
Today, most people choose the longer phrase because it sounds more natural in conversation. Still, overmorrow is fully legitimate and easy to understand once you know it. It is a good example of how English keeps old words, even when everyday usage fades.