If someone or something quietens down or if you quieten them down , they become less noisy or less active. ( mainly BRIT; in AM, usually use quiet down )
The labour unrest which swept the country last week has quietened down...
Somehow I managed to quieten her down...
Tom’s words before the match might also have quietened down our own supporters.
= calm down
PHRASAL VERB : V P , V n P , V P n (not pron)