Surname 曰弟 (曰弟 
) , all over the world, is a very rare last name. The family name 曰弟 is characteristic of Eastern Asia, particularly China, where it is an extremely rare surname. More prevalently, 曰弟 is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| 曰弟 | China |