Europe
欧 centers on the idea of Europe, used in compounds for European things. The older meaning of 'vomit' or 'cough up' is rare in modern Japanese.
Europe
Europe and the United States; Europe and America; the West
Northern Europe; Nordic countries; Scandinavia
Western Europe
Eastern Europe
Europe
Southern Europe
writing in a European language; European text; Roman letters
European-style; Western; Occidental
Japan Association for Trade with Russia & Central-Eastern Europe (ROTOBO)
Central and Eastern Europe
Central Europe
Asia and Europe; Eurasia
all Europe
Scandinavian design
Nordic person; Scandinavian; Northern European
Nordic Council
Stockholm school
Nordic Council
Norse mythology
欧 originally combined 区 (a container) with 欠 (a person with an open mouth), suggesting vomiting or coughing up. In modern Japanese it is used almost exclusively as a phonetic abbreviation for Europe.
The left side 区 looks like a map of Europe with its distinct borders, and the right side 欠 looks like a person opening their mouth in awe at the continent's wonders.
For オウ, imagine a European person saying 'Oh!' in surprise: Oh -> オウ, as they discover the beauty of Europe.