1) Epoch-making 2) Extremely important 3) Extremely significant 4) Highly significant 5) Historically significant 6) Important 7) Momentous 8) Of a historic interval 9) Of an era 10) Significant 11) Very influential 1) Eral 2) Significant 
• (a.) Belonging to an epoch; of the nature of an epoch.
Ep'o·chal adjective Belonging to an epoch; of the nature of an epoch. ' Epochal points.' Shedd. 
[adj] - highly significant or important especially bringing about or marking the beginning of a new development or era
epoch-making adjective highly significant or important especially bringing about or marking the beginning of a new development or era; `epochal decisions made by Roosevelt and Churchill`; `an epoch-making discovery`
of, pertaining to, or of the nature of an epoch. · extremely important, significant, or influential.
highly significant, especially bringing about a new era[Difficult words] highly significant, especially bringing about a new era