哥
カ, コ, あに, うた

big brother

JLPT0 G13 S0 F5000

As per 可# (shout/laugh/sing in a loud voice) doubled → *sing*. *Elder brother* is a borrowed meaning, the doubling of the pronunciation of the character 可 matching a babyspeak appellation for older brother in ancient China.

[Full Kanji Etymology List]