1. overt => covert ( c- [from com-, intensive prefix; com- => co- => c-] + overt, 它们两属于反义同源 ).
2. 而 covert 又是由 cover 的古法语形式的过去分词形式直接借用过来的，因此你可以将 covert 直接看做是 cover 的古法语形式的过去分词。
3. 反义同源词根：oper-/opert(过去分词形式)(operire "cover, close") aper-/apert(过去分词形式)(aperire "uncover, open").
4. 同源同义音变：aper-/apert(过去分词形式)(aperire "uncover, open") ==> over-/overt(过去分词形式)(古法语：overt, past participle of ovrir "uncover, open").
5. PIE prefix *ap- "off, away" + base *wer- "cover"; PIE prefix *op- "over" + base *wer- "cover".
6. 注意同源音变的区别：apert- => overt; copert- => covert; coper- => cover.

covert 暗中的

来自cover, 覆盖。

1. They have been supplying covert military aid to the rebels.

他们一直在暗地里向叛乱者提供军事支援。

2. The depth of covert racism in my own profession frightens me.

我所从事的职业中暗藏着如此深的种族主义偏见，这让我感到害怕。

3. The army carried out covert surveillance of the building for several months.

军队对这座建筑物进行了数月的秘密监视.

4. The deer fled to a covert.

鹿逃入丛林中.

5. Religion is often made the covert of crime.

宗教常成为罪恶的护庇所.