on the quiet, on the sly, without saying a word
Она втихомолку ушла с вечеринки раньше всех.
She quietly left the party before anyone else.
Дети втихомолку съели все конфеты.
The children secretly ate all the candy.
Он втихомолку взял деньги из ящика.
He took the money from the drawer on the sly.
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