Greek Language/Two-letter Vowels

Apart from the simple vowels of Greek alphabet depicted by one letter, there are also combinations of two vowels pronounced like one sound that is identical to the sound of some of the simple ones. These combinations are called “two-letter vowels” (Greek: δίψηφα φωνήεντα) and have their origin in ancient Greek, when they were pronounced as diphthongs (long vowels with different parts, each of which has different value) but as the language evolved, they were flattened to simple sounds. Diphthongs still exist in modern Greek. The combinations of vowels that are pronounced as diphthongs can be distinguished from those that are pronounced as a single sound.

Two-letter vowels	Pronunciation	Notes
αι	[e]	Pronounced the same as ε.
ει	[i]	Pronounced the same as ι, η and υ.
οι	[i]	Pronounced the same as ι, η and υ.
υι	[i]	Pronounced the same as ι, η and υ.
ου	[u]	Pronounced like loot or school.

Apart from the two-letter vowels listed above, there are also two more structures consisting of two vowels that are called "αυ and ευ combinations" (Greek: συνδυασμοί αυ και ευ). These combinations are pronounced [av] and [ev] respectively, when followed by a vowel or a voiced consonant (e.g. ευανάγνωστος, αύριο) and [af] and [ef] respectively, when followed by an unvoiced consonant (e.g. αυτοκίνητο, κατεύθυνση). letter