Tigris

As a proper noun referring to a specific geographic entity, this word is used exclusively to denote the river in Western Asia. It is almost always paired with the Euphrates in historical or geographical discussions regarding Mesopotamia, creating a conceptual dyad that represents the foundation of early urban civilization.

Because it is a unique proper name for a single river, it does not function as a common noun and is never used in a plural sense. It maintains a formal, academic register typical of history, geography, and archaeology.