washboard

noun

• 1a board made of ridged wood or a sheet of corrugated zinc, used when washing clothes as a surface against which to scrub them.
• a ridged or corrugated board used as a percussion instrument.
• [as modifier] denoting a man’s stomach that is lean and has well-defined muscles: guys with washboard stomachs washboard abdominal muscles
• [mass noun] North American a ridged, uneven road surface: a patch of washboard bounces the wheels around sixteen miles of washboard

• 2a board fixed along the side of a boat to prevent water from spilling in over the edge.

verb

• cause ridges to develop in (a road or road surface):a road left washboarded by winter frost