one large ...; a great ...; a major ...
Prefix used to emphasize scale or importance, often in formal or news contexts. Attaches to nouns to mean 'a single large-scale ...' or 'a major ...'.
The discovery caused a great sensation in the scientific community.
彼は一大決心をして留学した。
He made a major decision and went to study abroad.
The discovery became a major event in the scientific world.
That movie sparked a huge boom.
This field grew into a major industry.
major turning point; significant turning point
crushing blow; heavy blow; hard blow