兄分
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に
ぶ
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Meanings
1
sworn elder brother; senior brother figure
Refers to a man treated as an older brother in a hierarchical, often non-blood, relationship, such as in yakuza or traditional craftsman circles. Contrasts with 弟分 (sworn younger brother).
See also: 弟分
He is looked up to as the sworn elder brother within the group.
2
older male partner in a homosexual relationship
Used in some contexts to refer to the older or more senior male partner in a male homosexual relationship. This usage is less common and may be considered dated or specific to certain subcultures.
In that circle, he is sometimes called the older partner.