Cognomen 洪洙 (洪洙 
) , in all the world, is a very rare family name. The surname 洪洙 is habitual in Eastern Asia, particularly China, where it is an extremely rare surname. More prevalently, 洪洙 is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| 洪洙 | China |