splashboard

1. A structure that protects the upper part of a vehicle from splashes of mud.
2. Nautical. A screen on a boat to keep water from splashing onto the deck.
3. A board for closing a spillway or sluice.

A board which provides protection against water splashes, as behind a sink.

The noun has 2 meanings:

Meaning #1: protective covering consisting of a broad plank along a gunwale to keep water from splashing over the side
  Synonym: washboard

Meaning #2: protective covering consisting of a panel to protect people from the splashing water or mud etc.
  Synonyms: splasher, dashboard