[countable, usually singular] a sudden decrease in an amount or the value of sth
（价格、数量的）暴跌，骤减◆The group has announced a plunge in annual profits.
这个集团已宣布年度利润锐减。◆This increase reversed an earlier price plunge.
这增长扭转了早些时候的价格暴跌。 SYN drop ●take the ˈplunge (informal) to decide to do sth important or difficult, especially after thinking about it for a long time
（尤指深思熟虑後）果断行事，采取决定性步骤◆Even when you're ready to take the plunge, setting up a business is not easy.
即使你准备放手一搏，创业也并非易事。