godan verb (-mu), intransitive verb
fall silent; clam up; sink into silence
Describes someone who stops talking and becomes completely silent, often due to embarrassment, anger, or deep thought. The compound verb 黙り込む emphasizes the action of going into a state of silence.
彼は質問に答えられず、黙り込んでしまった。
Unable to answer the question, he fell completely silent.
会議中、彼
During the meeting, she suddenly clammed up.