doniosły wielkiej wagi in inglese:

What was going on in Ukraine was clearly momentous

a momentous decision. event, occasion, journey, performance

It was the perfect quote for such a momentous occasion.

He took a momentous decision. He resigned from his job.

This momentous decree came as a great beacon light of hope to millions of Negro slaves who had been seared in the flames of withering injustice.

The discovery will have a momentous effect on the treatment of cancer.