1. (价格、利润或汇率)暴跌，急剧下降
If prices, profits, or exchange rates nosedive, they suddenly fall by a large amount.

2. (名声或事业)一落千丈，急转直下
If something such as someone's reputation or career nosedives, it suddenly gets much worse.

1. a steep nose-down descent by an aircraft

Synonym: divenose dive

2. a sudden sharp drop or rapid decline

e.g. the stock took a nosedive