xiǎo​dì

humble I

小弟 xiǎo​dì
humble I noun
a self-referential term used by a male to refer to himself modestly in front of others
younger brother noun
one's younger brother or a younger male peer

He is my younger brother, three years younger than me.

Frequency

Movie subtitles
6.83 per million appears in 3% of films
Written text
8.11 per million

Sources

Definitions
CC-CEDICT