留洋

洋 ('ocean; Western lands') makes this a classic late-Qing / Republican-era word for going abroad — think 留洋学生 of the 1920s. In modern Mandarin 留学 has replaced it for education; 留洋 now mostly appears in sports journalism about Chinese athletes playing overseas.

Slightly literary or journalistic. For 'study abroad' in normal speech, 留学 is standard. 留洋 in sports context is neutral and current.