by accident 偶然；意外地；不小心

【例句】
I met the man quite by accident, and we began a conversation, I learnt he was an old seaman12 who kept an inn13.

我十分偶然地碰上这个人，然后我们就聊起来。我了解到他是个老水手，现在在这里开一家旅馆。

He hit upon the solution to the problem almost by accident.
他几乎是偶然地找到了解决问题的办法。