唯恐

lest

for fear that

for fear of

他们那时听不到她的消息，唯恐发生了最糟的事。
When they did not hear from her, they feared the worst.

我突然停住，唯恐他会认为我是在炫耀。
I stopped suddenly in case he should think that I was showing off.

他继续往下谈，唯恐显露出内心的不安来。
He went on talking, lest he should expose his uneasiness.

他们低声说话，唯恐被别人听见。
They spoke in whispers lest they should be heard.

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