also: ぼんなか
noun
good friend from a gambling den
Slang term for a close friend one has become acquainted with at a gambling den; rare and limited to that subculture.
あいつは俺のボンナカで、よく一緒に賭場に行くんだ。
He's my bonnaka; we often go to the gambling den together.
ボンナカ同士で金の貸し借りはしないほうがいい。
It's better not to lend or borrow money between bonnaka.
仲間 is a general term for companion or colleague, while ボンナカ specifically refers to a friend made in a gambling context.
ダチ is a casual slang term for friend, but lacks the gambling-den association of ボンナカ.
Likely a compound of 盆 (bon, 'gambling den') and 仲 (naka, 'relationship'), with the reading ボンナカ reflecting slangy katakana usage. The exact origin is uncertain but clearly tied to gambling subculture.