The two parties reached a secret agreement long ago.

双方早有默契。

《新英汉大辞典》

Collusion in judicial proceedings is a secret agreement.

在司法程序中，通谋是指一项秘密协议。

youdao

Mr. Knightley, in his turn, saw signs of some secret agreement between Jane Fairfax and Frank Churchill.

而奈特利先生则觉察到简和邱吉尔之间已有某种秘约。

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After the political agreement was signed scores of MDC supporters and rights activists were kidnapped and held in secret locations for weeks and months.

VOA: standard.2009.09.15

Whether or not there was a secret agreement, this is what actually happened.

ECONOMIST: The unchosen people | The

After Silver censured Lopez, the speaker said he won't again enter into secret agreement to settle such claims, saying the public deserves more transparency.

WSJ: NY ethics panel acts in Lopez sex harassment case

It turns out that, in 1995, Vice President Al Gore signed a secret agreement with then-Russian Prime Minister Viktor Chernomyrdin "which essentially exempted Russia from American sanctions on arms deliveries to Iran, " sanctions that were ironically required pursuant to a statute Mr. Gore co-sponsored when he served in the U.S. Senate.

CENTERFORSECURITYPOLICY: When Security Fails