Definition: The Tigris is one of the two main rivers of Mesopotamia (modern Iraq). The Tigris is the river to the east (towards Persia [modern Iran]); the Euphrates, to the west. The Tigris runs from Lake Hazar, in the Taurus Mountains, in Turkey, joins the Euphrates, and flows into the Persian Gulf. The Encyclopedia Britannica says the Tigris is 1,180 miles (1,900 km) in length. Irrigation through seven millennia has changed the course of the river.
Alternate Spellings: From the Encyclopedia Britannica: Sumerian: Idigna; Akkadian: Idiklat; biblical: Hiddekel; Arabic: Dijlah; Turkish: Dicle
Examples:The Tigris and Euphrates are the two rivers between which Mesopotamia ('the land between two rivers') ran.
"11 Semiramis founded other cities also along the Euphrates and Tigris rivers, in which she established trading-places for the merchants who brought goods from Media, Paraetacenê, and all the neighbouring region. For the Euphrates and Tigris, the most notable, one may say, of all the rivers of Asia after the Nile and Ganges, have their sources in the mountains of Armenia and are two thousand five hundred stades apart at their origin, 2 and after flowing through Media and Paraetacenê they enter Mesopotamia, which they enclose between them, thus giving this name to the country. After this they pass through Babylonia and empty into the Red Sea [the Persian Gulf]."
"And the name of the third river is Hiddekel [Tigris]: that is it which goeth toward the east of Assyria. And the fourth river is Euphrates."
On the location of the Garden of Eden, From KJV Genesis II