17.

black market
黑市

[双语解释]

A market place where illegal or hard-to-get items are sold or where money is illegal exchanged.
非法或紧俏物资的销售点，或者非法换汇的地方。

例句：

Gangs are buying assault weapons on the black market.
黑帮总在黑市购买攻击性武器。