If the virus had been capable of spreading through the air, or if one infected person had unknowingly entered a large population center, Ebola might have become a worldwide epidemic.
出自-2013年6月听力原文
柯林斯高阶英汉双解学习词典释义
ADV
未意识到地；不知不觉地；无意中
If someone does something unknowingly, they do it without being aware of it.
例句
...if people unknowingly move into more contaminated areas of the river.如果人们在不知情的情况下搬到了河流污染更严重的地区...the extent to which the workforce colludes knowingly or unknowingly with such criminal activity...在何种程度上职工有意或无意地参与到这样的犯罪活动中