Danube
"Danube" is an Old European river name derived from a Proto-Indo-European "*dānu". Other river names from the same root include the Dunaj, Dzvina/Daugava, Don, Donets, Dnieper, Dniestr, Dysna, Tana and Tuoni. In Rigvedic Sanskrit, "dānu" means "fluid, drop", in Avestan, the same word means "river". In the Rigveda, "Dānu" once appears as the mother of Vrtra, "a dragon blocking the course of the rivers." The Finnish word for Danube is Tonava, which is most likely derived from the word for the river in Swedish and German, "Donau". Its Sámi name "Deatnu" means "Great River". It is possible that "dānu" in Scythian as in Avestan was a generic word for "river": "Dnieper" and "Dniestr", from "Danapris" and "Danastius", are presumed to continue Scythian "*dānu apara" "far river" and "*dānu nazdya-" "near river", respectively.
Kivertsi
The name ”Kivertsi” historians associate with the name of an ancient tribe called ”Tivertsi” that lived on the banks of the Dniester River at the mouth of the Danube. At the end of the 11th and the beginning of the 12th century under the pressure of neighbour nomadic tribes Tivertsi moved north. Divided into smaller groups the tribe has spread and settled in Volyn. Over time, the name mutated into ”Kivertsi” and was assigned to the place of settlement of the tribe.