Where does “eiste” come from?

eiste (Middle Irish) comes from Old Irish essi, from Old Irish a, from Proto-Celtic *ā, from Proto-Indo-European ō — oh, ah.

Ancestry of “eiste”, step by step

StepLanguageWordMeaning
1Old Irishessithird-person singular feminine of as
2Old Irishanominative/accusative singular neuter of in; that...
3Proto-Celtic*āO (vocative particle)
4Proto-Indo-Europeanōoh, ah

Words derived from “eiste”

Every word from Proto-Indo-European ō →Every word from Proto-Celtic *ā →Every word from Old Irish a →