An Asian river; a tributary of the Euphrates River WordNet 3.0 & Open English WordNet

The Tigris is the eastern of the two great rivers that define Mesopotamia, the other being the Euphrates. Wikipedia

Eastern member of the two great rivers that define Mesopotamia. Wikipedia Disambiguation

River flowing from Turkey through Iraq and Syria Wikidata

The eastern member of the pair of great rivers that define Mesopotamia and which flows from Anatolia through Iraq into the Persian Gulf. OmegaWiki

A river in Southwest Asia flowing 1,150 miles east-southeast from the Armenian Highland in Turkey through Iraq. It forms the eastern edge of classical Mesopotamia. It unites with the Euphrates River to form the Shatt al-Arab before flowing into the Persian Gulf. Wiktionary

River in Southwest Asia. Wiktionary (translation)