momentous
adj.very important because it will have a big effect on the future. You use this to describe a major event or decision.
adj.of great importance or significance, especially in its bearing on future events. Often used to describe historical turning points or life-changing decisions.
“The two countries signed a momentous peace treaty today.”
“Graduating from university is a momentous occasion that marks the start of a new chapter in life.”
“The discovery of the new vaccine was a momentous achievement that promised to alter the course of global public health for generations to come.”
Typically used as an attributive adjective before a noun like 'decision', 'occasion', or 'event'.
Learners confuse 'momentous' (important) with 'momentary' (lasting only a short time).
“Has it happened before that such a momentous case with potential ramifications for voting has come to the Supreme Court this close to an election?”
“As for Trent, our plucky project manager, the launch marks the end of a momentous 12 months.”
From moment (“weight, importance”) + -ous.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.