How do you say brother in Mandarin?

There are a few ways to say "brother" in Mandarin, depending on the context:

Formal:

* 哥哥 (gēge) - Older brother

* 弟弟 (dìdi) - Younger brother

Informal:

* 哥 (gē) - Older brother (used when addressing your brother)

* 弟 (dì) - Younger brother (used when addressing your brother)

* 兄弟 (xiōngdì) - Brothers (plural, can be used for close friends)

Family terms:

* 兄 (xiōng) - Older brother (used in formal writing)

* 弟 (dì) - Younger brother (used in formal writing)

The specific term you use depends on the relationship between the speaker and the brother, the age difference, and the level of formality.