Strictly speaking, the word "OU" has no classical idiom.
In modern idioms, there are the following two idioms that contain the word "欧".
European wind and beautiful rain: ①A metaphor for the politics, economy and culture of Europe and the United States. ② Metaphor for European and American aggression.
European wind and moyu: a metaphor for the invasion of ideas and culture from Europe and America
These two idioms basically have the same meaning.
In addition, the word "OU" is actually the same as "贴" in ancient times, which means singing.
There is also an idiom with the word "贴".
Praise one’s merits and praise one’s virtues: I still sing songs in praise of one’s merits and virtues.
I don’t know why you ask this question. If you are thinking of your online name, it must have a European name in it.
If you can use an idiom with the same sound as ou to name it, just replace one word.
For example, "No one is alone, there is a coincidence", "A shadow travels alone", etc. are all acceptable.