Polite term for one's own brother-in-law (spouse's older brother or older sister's husband). Used when referring to him in conversation or addressing him directly.
I heard that my brother-in-law is getting married next month.
How are you, brother-in-law?
Formal, often used in official documents or formal introductions. Less common in casual conversation.
Compound of 義理 (giri, 'duty, obligation, in-law relationship') + の (no, possessive particle) + お兄さん (oniisan, 'older brother', polite). The prefix お adds politeness.