замолча́ть

fairly common #1898C1

verbperfective imperfective is молча́ть

1.
to fall silent, to become silent, to stop speaking
Он вдруг замолча́л и посмотре́л в окно́.
He suddenly fell silent and looked out of the window.
Perfective; describes the moment of breaking off speech or of a sound ceasing.
2.
(rare) to hush up, to suppress (news), to keep quiet about
Газе́ты постара́лись замолча́ть э́ту исто́рию.
The newspapers tried to hush the story up.
Transitive, with a direct object: to deliberately keep a fact from becoming known.

Examples

Он скомандовал остановиться и замолчать.
He ordered everyone to stop and be quiet.
Он властно приказал всем замолчать.
He imperiously ordered everyone to be quiet.
Старик промолвил что-то и замолчал.
The old man said something and fell silent.
Возьми́ его и замолчи́.
Take it and shut up.
Том не знал, когда замолча́ть.
Tom didn't know when to shut up.
Он важно изрёк последнюю фразу и замолчал.
He pompously uttered the last sentence and fell silent.
Том сказа́л Мэри замолча́ть.
Tom told Mary to shut up.
Том веле́л мне замолча́ть.
Tom told me to stop talking.

Imperative
ты	замолчи́
вы	замолчи́те

Active present	-
Active past	замолча́вший	silent (having fallen silent), having stopped speaking
Passive present	-
Passive past	замолчанный	unmentioned, unsaid, hushed up, passed over in silence
Gerund present	-
Gerund past	замолча́в замолчавши	while doing (past)