WATERSHED

(BIG CHANGE) [noun] [U] - an event or period which is important because it represents a big change and the start of new developmentsHis biographical essay on Mozart marked a watershed in the development of biographical studies.1969 was a watershed in her life - she changed her career and changed her partner.John Kennedy's presidential campaign in 1960 was a watershed.'Cabaret' was a watershed musical which seems to have influenced the shape and structure of musicals ever since.