Iotified vowel

In Slavic languages, iotation /joʊˈteɪʃən/ is a form of palatalization that occurs when a consonant comes into contact with a palatal approximant /j/ from the succeeding morpheme. The /j/ is represented by iota (ι) in the Cyrillic alphabet and the Greek alphabet on which it is based. For example, ni in English onion has the sound of iotated n. Iotation is a distinct phenomenon from Slavic first palatalization in which only the front vowels are involved, but the final result is similar.

Iotation occurs when a labial (/m/, /b/), dental (/n/, /s/, /l/) or velar (/k/, /g/, /x/) consonant comes into contact with a iotified vowel, i.e. one preceded by a palatal glide /j/. As result, the consonant becomes partially or completely palatalized. In many Slavic languages, iotated consonants are called "soft" and the process of iotation is called "softening".

Iotation can result in a partial palatalization so the centre of the tongue is raised during and after the articulation of the consonant. There can also be a complete sound change to a palatal or alveolo-palatal consonant. This table summarizes the typical outcomes in the modern Slavic languages:

According to most scholars, the period of iotation started approximately in the 5th century, in the era of Proto-Slavic, and it lasted for several centuries, probably into the late Common Slavic dialect differentiation. Here are examples from the early stage:

...
Wikipedia