Itacism

Iotacism (Greek: ἰωτακισμός, iotakismos) is the process by which a number of vowels and diphthongs in Ancient Greek converged in pronunciation so they all now sound like iota ([i]) in Modern Greek. In the case of the letter eta specifically, the process is known as itacism (from the resulting pronunciation of the letter's name as [ˈita]).

Ancient Greek had a broader range of vowels (see Ancient Greek phonology) than Modern Greek does. Eta (η) was a long open-mid front unrounded vowel /ɛː/, and upsilon (υ) was a close front rounded vowel /y/. Over the course of time, both vowels came to be pronounced like the close front unrounded vowel iota (ι) [i]. In addition, certain diphthongs merged to the same pronunciation. Specifically, Epsilon-iota (ει) initially merged with eta (η) while, later, omikron-iota (οι) and upsilon-iota (υι) merged with upsilon (υ). As a result of eta and upsilon being affected by iotacism, so were the respective diphthongs.

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