弟 (Kanji for younger brother)

Onyomi

TEI, DAI

When my younger brother gets horny he TAKES a bow like Cupid and shoots you and you DIE.

He's passionate but unfortunately not gifted with a sense of poetic metaphor.

おとうと	someone's younger brother (say if you're talking to your friend's younger brother) ★★★★☆

兄弟(きょうだい)

siblings ★★★★★
兄 (older brother) + 弟 (younger brother) = 兄弟 (siblings)

siblings (not just brothers)

弟子(でし)

student ★☆☆☆☆ FP F
弟 (younger brother) + 子 (child) = 弟子 (student)

student (more formal, ususally used with the name of the institution: Harvard弟子、 Waseda 弟子）