The motion of water or other liquid returning seaward after a wave has broken on the shore. The backwash of the wave pulled the sand from under my feet.
A backward flow or movement, often used metaphorically to describe the negative consequences or aftermath of an event. The backwash of the scandal affected the company's reputation for years.
A flow of liquid sent backward through a filter to cleanse it, or the liquid used in this process. The filter's backwash was cloudy, showing how much debris had been trapped.