We don't have synonyms for boyar yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are boar, boyer and bolar.
(n) :
(historical) A member of a rank of aristocracy (second only to princes) in Russia, Ukraine, Belarus, Bulgaria, North Macedonia, Serbia and Romania.
(n) :
(historical) A member of a rank of aristocracy (second only to princes) in Russia, Ukraine, Belarus, Bulgaria, North Macedonia, Serbia and Romania.