无意中；意外unintentional; unplanned

• 偶然相遇

  meet accidentally

• 偶然听到

  happen to hear

• 偶然想起

  happen to think of

• 偶然有机会

  happen to get an opportunity

• 偶然的错误

  accidental error

• 事出偶然。

  This situation was unexpected.

• 这是偶然的事。

  This was unintentional.

• 他这样办决不是偶然的。

  He definitely didn't do it this way accidentally.

• 我这也是偶然知道的。

  I just happened to find this out.

参见：偶尔