Slavic liquid metathesis and pleophony
The Slavic liquid metathesis refers to the phenomenon of metathesis of liquid consonants in the Common Slavic period in the South Slavic and West Slavic area. The closely related corresponding phenomenon of pleophony (also known as polnoglasie or full vocalization) occurred in parallel in the East Slavic languages.
Source: Wikipedia — Slavic liquid metathesis and pleophony (CC BY-SA 4.0)