What is "vainius"

Vainius or Voin (died between 1338 and 1342) was the Prince of Polotsk from 1315 to his death. Very little is known about Vainius, brother of Gediminas, Grand Duke of Lithuania. He is mentioned in written sources in 1324 for the first time. In 1326 he, already as Prince of Polotsk, signed a treaty with the Livonian Order and Novgorod. His only known son Liubko died in 1342 during fights with the Livonian Order.