From Longman Dictionary of Contemporary Englishplunge in (also plunge into something) phrasal verb1 START DOING somethingto 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.► see thesaurus at put → plunge→ See Verb table
Examples from the Corpus
plunged ... knife• He plunged the knife into the boiling water and speared one slice. 