noun
completely deaf
Refers to total deafness; often used in a somewhat blunt or colloquial manner. The term can be considered insensitive in modern usage.
彼は事故でかなつんぼになってしまった。
He became completely deaf due to an accident.
聾 (つんぼ) is a more general term for deafness, while 金聾 (かなつんぼ) specifically means total deafness. 聾 is also considered a blunt or dated term.
The origin is uncertain. The kanji 金 (metal) and 鉄 (iron) may be used metaphorically to suggest complete or solid deafness, but this is speculative.