to (cause someone or something to) move or fall suddenly and often a long way forward, down, or into something:
+ adv./prep.
She lost her balance and plunged 100 feet to her death.
她没有站稳，从 100 英尺的高处跌下摔死了。
~ sb/sth + adv./prep.
The earthquake plunged entire towns over the edge of the cliffs.
地震将整座整座的城镇掀到悬崖之下。
to start doing sth in an enthusiastic way, especially without thinking carefully about what you are doing 热情投入；贸然行动
She was about to plunge into her story when the phone rang.
她刚要开始大谈她的经历，电话响了。
He’s always plunging in at the deep end (= becoming involved in difficult situations without being well enough prepared).
他总是贸然行动，屡屡陷入困境。