To Shut Up, To Be Silent
intransitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means shut up so the verb vocab version is to shut up.
だまる
You need to dam (だま) your mouth shut and shut up.
どうしたの？どうして黙っているの？
What’s the matter? Why are you so quiet?