noun, noun or participle which takes 'suru', intransitive verb
defer to as an older brother; treat with brotherly respect
Rare literary expression for treating someone with the deference and respect due to an older brother. Often used in classical or formal contexts.
彼は年上の友人を兄事している。
He defers to his older friend as if he were an older brother.
Compound of 兄 (older brother) and 事 (to serve, to treat as). The exact historical derivation is uncertain, but the meaning is transparent from its components.