plunge in ( also plunge into something ) phrasal verb ( see also ↑ plunge )
1 . to start talking or doing something quickly and confidently, especially without thinking about it first:
It’s a difficult situation. You can’t just plunge in and put everything right.
‘I don’t agree,’ she said, plunging into the conversation.
2 . to jump or ↑ dive into water:
He stripped off and plunged into the sea.
3 . plunge something ↔ in ( also plunge something into something ) to push something firmly and deeply into something else:
He opened the bag and plunged his hand in.
Plunge the pasta into boiling water.
Repeatedly she plunged the knife into his chest.