Refers to one's spouse's older brother or the husband of one's older sister. A respectful term used when addressing or referring to him.
I heard my brother-in-law is getting married next month.
I had my brother-in-law look after the children.
older stepbrother
Used for an older stepbrother (a brother through remarriage of a parent). The same respectful term applies.
My new older stepbrother is very kind.
Standard respectful term for an older brother-in-law or older stepbrother. The kanji 義兄 explicitly marks the 'in-law' or 'step' relationship.
Commonly used in practice when the in-law/step relationship is clear from context, but can also mean one's own older brother. Use お義兄さん for disambiguation.
Polite prefix お + 義兄 (ぎけい, 'brother-in-law') + honorific suffix さん. The reading おにいさん is a gikun (meaning-based reading) applied to the kanji 義兄.