What is a diphthong? Diphthongs are vowel combinations. In Lesson 4, we learn to pronounce Greek words with diphthongs. Diphthongs are formed when two vowels "smash together" to form a single sound, like "ee" in "seed" or "oi" in "oil." Greek diphthongs are easy to mispronounce, because in English we often pronounce vowel combinations differently. For instance, "oi" in "oil" is actually pronounced like "ee" in "seed." Thus, the Greek word οικος (oikos) is pronounced "ee-kos." We also learn our first Greek words that are not names or places in this lesson. Here is the vocabularly list for this lesson: ευχαριστω - thank you αυτο - itself / it οικος - house In the next lesson, we will dive into John's Gospel and look at the actual New Testament Greek.