/ ˈwɔːtəʃed; NAmE ˈwɔːtərʃed; ˈwɑːt-/ noun
1.
[ C ] watershed (in sth) an event or a period of time that marks an important change :
The middle decades of the 19th century marked a watershed in Russia's history.
2.
[ C ] a line of high land where streams on one side flow into one river, and streams on the other side flow into a different river
3.
the watershed [ sing. ] (in Britain) the time before which programmes that are not considered suitable for children may not be shown on television :
the 9 o'clock watershed
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WORD ORIGIN
early 19th cent.: from water + shed in the sense ridge of high ground (related to the verb shed ), suggested by German Wasserscheide .