also: おとうと
younger brother-in-law
Refers specifically to a male in-law in a younger-brother position: one's spouse's younger brother, or one's younger sister's husband.
My wife's younger brother, that is, my brother-in-law, is coming this weekend.
My younger sister's husband is also my brother-in-law.
younger stepbrother
Rare use for a younger stepbrother. In everyday speech, 義理の弟 is often clearer and more natural for this relationship.
After my father remarried, I got a younger stepbrother.
Her younger brother-in-law is a college student.
This person is my younger brother-in-law.
義弟 refers to a younger brother-in-law, while 義兄 refers to an older brother-in-law.
実弟 refers to a younger brother by blood, while 義弟 refers to a younger brother by marriage or adoption.
Standard Sino-Japanese reading for this kanji spelling; used for a younger brother-in-law and, more rarely, a younger stepbrother.
Attested special meaning-based reading; in ordinary text 義弟 is normally read ぎてい unless furigana or context indicates otherwise.
A compound of 義, here indicating a non-blood family relationship such as marriage or adoption, and 弟, 'younger brother.' The regular reading is Sino-Japanese ぎてい; おとうと is a special meaning-based reading noted.