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secret; private; surreptitious
窃かに進められていた計画がついに明るみに出た。
The plan that had been carried out in secret finally came to light.
窃かに想いを寄せていた人に告白する勇気が出た。
I found the courage to confess to the person I had secretly admired.
窃かに涙を流しながらも表では笑顔を見せていた。
She showed a smile in public while secretly shedding tears.