Epochal is an adjective that means highly momentous or important.

Our word of the day has its origin in the Greek word epoche (EP oke) which means ‘a fixed point in time.’ When something is described as an epoch, we mean it is an important point in time. Epochal is the adjective version of that. For example: There was something epochal about that last day of school. I had the feeling that everything that followed that momentous occasion would be different.