What is "erdvilas"

Erdvilas (Erdywił, Ердивил, Erdiwił, Erdwil) was one of the 21 early dukes of Lithuania who signed a treaty with Galicia–Volhynia in 1219. He and Vykintas are the two dukes of Samogitia mentioned in the treaty. This is supported by the fact that the eastern part of Samogitia supported King of Lithuania Mindaugas, while the western part, ruled by Vykintas, was more hostile. That is the only mention of him in written sources. Few historians consider that Treniota, Mindaugas' nephew, was son of Erdvilas. However more prefer Vykintas as Treniota's father.