Ereyesterday is a real English word that means the day before yesterday. In other words, it refers to two days ago. Most modern English speakers do not use it in everyday conversation, but it does appear in dictionaries and older writing.
The word is easy to understand once you compare it with more familiar time words:
- yesterday: one day ago
- ereyesterday: two days ago
For example, you could say, I saw him ereyesterday. That sentence means I saw him the day before yesterday. Both are correct, but the longer phrase is much more common in current English.
If you want natural everyday wording, say the day before yesterday. If you are reading older texts or enjoy unusual vocabulary, ereyesterday is a useful word to know. It is a good example of how English sometimes has a single rare word where modern speakers prefer a simple phrase instead.