noun, adjective · a significant occurrence, particularly one concerning national politics, war, or a change of regime

关心国家大事是每个公民的责任。

adjective, noun · an important personal or social event, specifically life rituals such as weddings or funerals

结婚是人生的一件大事。

noun · to perform an action in a grand manner or on a large scale

媒体对这次科研突破进行了大事宣传。