elder brother; my dear brother
Archaic, respectful term for one's own elder brother, used in classical or literary contexts. Not used in modern everyday speech.
In an old letter, it was written, 'I pray for my dear elder brother's health.'
The prefix 阿 (a) is an archaic honorific or familiar prefix, and 兄 (kei) is a Sino-Japanese reading for 'elder brother'. The exact historical derivation is uncertain, but the combination is a classical respectful term.