epoch-making; transition between eras
Refers to a major turning point that marks the beginning of a new era. Often used in the compound 画期的 (かっきてき, 'epoch-making'). As a standalone noun, it is somewhat literary.
See also: 画期的
This invention marks an epoch in science.
The Meiji Restoration was a major turning point in Japanese history.
That discovery marked a turning point in the history of science.
画期 is a literary noun for an era-defining turning point in history, whereas 転機 is the everyday word for a turning point in a person's life or a situation.
groundbreaking; revolutionary; epoch-making
Standard modern spelling.
Rarely used kanji form; 劃 is an older variant of 画.
From 画 (かく, 'divide') + 期 (き, 'period'). The kanji 画 originally meant 'to draw a line', hence 'to demarcate', giving the sense of dividing historical periods.