Eureka (word)
"Eureka" comes from the Ancient Greek word "heúrēka", meaning "I found (it)", which is the first person singular perfect indicative active of the verb "heuriskō" "I find". It is closely related to heuristic, which refers to experience-based techniques for problem solving, learning, and discovery.
Erebuni Fortress
The Circassian historian Amjad Jaimoukha gives an alternative etymology, however: "eri" (referring to the Èrs, the people living in the area) + "buni". "Buni" comes from the Nakh root which spawned the Chechen word "bun" meaning shelter or cabin; the root however simply means lair or shelter. With its Indo-European roots "bun" initially derives from the Armenian word "buyn" (բույն) for "nest" or "lair". From Proto-Indo-European *bʰeuH-no-, from *bʰeuH- (“to be; to grow”). Cognates include Sanskrit भुवन (bhúvana, "world"), Albanian bun ("shepherd's hut") and Middle Persian بن bun ("bottom"). It may have spawned the word "van" in Armenian (a language with a strong Urartian substratum), albeit possibly through different roots (Urartian "biani" rather than Èr "buni") which similarly means shelter. "Van" as a root is also present in numerous other placenames in historical Armenia, including the city Van, Lake Sevan, and Nakhichevan, so it is probable that the "van" in "Yerevan" is another direct translation of the root. Jaimoukha states furthermore that the name of the Èr also serves as the root for the Arax valley (the Erashki gorge) and for the Medieval Georgian name used in the "Georgian Chronicles" for Lake Sevan- "Lake Ereta".