Momentous (adjective)

Of great importance; significant.

Origin:

From moment + -ous.

Examples:

1. The decision was momentous and would affect the company for years to come.
2. It was a momentous occasion for the family to gather and celebrate.
3. The momentous event was celebrated with a parade and fireworks.
4. The momentous discovery revolutionized the field of science.
5. The momentous achievement was marked with a ceremony and speeches.