Simple past tense and past participle of quieten.(verb)
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Use "quietened" in a sentence
"But it was a measure of how Chelsea's players responded that the Terry-ometer soon quietened down."
"The mare fidgeted, but Alex quietened her with his whispered words and his gentle hands."
"Things quietened down a bit in the second episode, which saw Paul seeing April, a 23-year-old student with cancer, though the session had enough unresolved sexual tension for you to reckon there was a world of hurt and pain to be opened up in the weeks to come."