1.
illegal transaction; black market deal; underground dealing
A transaction conducted secretly and illegally, outside official or regulated channels. Includes black market sales, illicit trading, and under-the-table deals.
Composed of 闇 (darkness, secrecy) + 取引 (transaction, deal). The prefix 闇 is productive for illegal/underground activities: 闇ルート (illegal channel), 闇金融 (loan sharking), 闇市 (black market). Historically associated with the postwar black market (闇市). In modern usage, appears in news about organized crime, smuggling, and online illegal sales.