17.

black market
黑市

[雙語解釋]

A market place where illegal or hard-to-get items are sold or where money is illegal exchanged.
非法或緊俏物資的銷售點，或者非法換匯的地方。

例句：

Gangs are buying assault weapons on the black market.
黑幫總在黑市購買攻擊性武器。