болꙗринъ

Perhaps from Proto-Slavic *bojь (“struggle, fight”), or related to *bol (“great”), found in the first element of большой (bolʹšoj, “great”).^[1] (Can this⁽⁺⁾ etymology be sourced?)

Watkins instead proposes a Bulgar origin, from ΒΟΥΗΛΑ (bouēla), *boyla-er (“nobleman”), noting also Old Turkic 𐰉𐰆𐰖𐰞𐰀 (boyla, buyla)^[2] (Can this⁽⁺⁾ etymology be sourced?)

болꙗринъ • (boljarinŭ) m

1. aristocrat, nobleman, boyar
   • from the Homily against the Bogumils, 1643-1649:

     хоулѧще богатꙑѩ, царь ненавидѧтъ, рѫгаѭтъ сѧ старѣишинамъ, оукарꙗѭтъ болꙗрꙑ, мрьзькꙑ богоу мьнѧтъ работаѭщѧѩ цѣсарю, и вьсꙗкомоу рабоу не велѧтъ работати господиноу своѥмоу.

     xulęšte bogatyję, carĭ nenavidętŭ, rǫgajǫtŭ sę starěišinamŭ, ukarjajǫtŭ boljary, mrĭzĭky bogu mĭnętŭ rabotajǫštęję cěsarju, i vĭsjakomu rabu ne velętŭ rabotati gospodinu svojemu.

     They scorn the rich, they hate the Tsars, they ridicule their superiors, they reproach the boyars, they believe that God looks in horror on those who labour for the Tsar, and advise every serf not to work for his master.