noun
Geographical term for the line separating drainage basins; used in geography and environmental contexts.
この山脈が太平洋側と日本海側の分水線になっている。
This mountain range forms the watershed between the Pacific side and the Sea of Japan side.
Compound of 分水 (dividing water) + 線 (line). The exact historical derivation is uncertain; the spelling is conventionally associated with the geographical meaning.