еси

• ѥси (jesi)[1][2][3][4] (year 1180±20)
• єси (esi)[5] (year 1380±20)
• ѥсѣ (jesě)[6] (year 1385±15)
• ѥсь (jesĭ)[7] (year 1370±30)

First attested as еси (esi) in year 1063±13. From Proto-Slavic *esi.

еси (esi)

1. second-person singular present of бꙑти (byti)

• Zaliznyak, Andrey (2004), “бꙑти”, in Древненовгородский диалект [Old Novgorod dialect] (Studia philologica) (in Russian), 2nd edition, Moscow: Languages of Slavic Cultures, →ISBN, page 715 of 872
• Древнерусские берестяные грамоты [Birchbark Literacy from Medieval Rus] (in Russian), http://gramoty.ru, (please provide a date or year)document № 915
• Древнерусские берестяные грамоты [Birchbark Literacy from Medieval Rus] (in Russian), http://gramoty.ru, (please provide a date or year)document № 909
• Древнерусские берестяные грамоты [Birchbark Literacy from Medieval Rus] (in Russian), http://gramoty.ru, (please provide a date or year)document № 109

From Proto-Slavic *esi.

• IPA^(key): [(j)ɪˈsʲi]

еси́ • (jesí)

1. (obsolete) second-person singular present indicative imperfective of быть (bytʹ); (you) are, (thou) art