wa•ter•shed \ˈwȯ-tər-ˌshed, ˈwä-\ noun. 1803. 1 a : divide b : a region or area bounded peripherally by a divide and draining ultimately to a particular watercourse or body of water.
Merriam-Webster
“What it means depends on where you’re standing,” says Michael Quinion. Originating as a purely scientific word around 1800, watershed meant “the imaginary line that separates two river systems.” The English word was borrowed from the German Wasserscheide. Shed or scheide is an old word meaning division, split, or separation. “In North America, the word watershed often means not the dividing line, but the river catchment areas on either side of the ridge, the whole land area that drains into a particular river. How the sense shifted isn’t clear.” Quinion speculates that, “The difference in sense explains why Americans don’t use the figurative sense of the word as much as the rest of us do.”
World Wide Words: Michael Quinion writes on international English from a British viewpoint.
