a dangerous area of strongly moving water in the sea, where two or more currents (= water moving in a particular direction) meet

The riptide was pulling a surfer under. 激流把一个冲浪的人拖到水下。

a strong negative feeling or force that is difficult to control

Warnings about terror attacks sent a riptide of anxiety through the nation. 关于恐怖袭击的警告在全国掀起了一股焦虑的浪潮。