boyar
A member of a rank of aristocracy (second only to princes) in Russia, Ukraine, Belarus, Bulgaria, North Macedonia, Serbia and Romania.
historical
Boris had abdicated in 889, leaving the throne to his son Vladimir, who had immediately identified himself with the boyar aristocracy which Boris had done his utmost to crush.
Where it comes from
From Russian боя́ре (bojáre), plural of боя́рин (bojárin).
Adapted from the Wiktionary entry boyar (CC BY-SA 4.0).