lowering

In phonology and phonetics, raising is a sound change in which a vowel or consonant becomes higher or raised, meaning that the tongue becomes more elevated or positioned closer to the roof of the mouth than before. The opposite effect is known as lowering. Raising or lowering may be triggered by a nearby sound, when it is a form of assimilation, or it may occur on its own.
In i-mutation, a front vowel is raised before /i/ or /j/, which is assimilation.
In the Attic dialect of Ancient Greek and in Koine Greek, close-mid /eː oː/ were raised to /iː uː/. The change occurred in all cases and was not triggered by a nearby front consonant or vowel. Later, Ancient Greek /ɛː/ was raised to become Koine Greek [eː] and then [iː]. For more information, see Ancient Greek phonology § Vowel raising and fronting
In Czech, the alveolar trill /r/ was raised before /i/ to become the raised alveolar trill /r̝/, spelled ⟨ř⟩ as in ⟨Dvořák⟩. That is a form of palatalization, and it also occurred in Polish in which it became a simple sibilant fricative /ʐ/ (spelled ⟨rz⟩ or ⟨ż⟩) around the 16th century. The pronunciation [r̝] in Polish is considered to be nonstandard and is used only by some older speakers.

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