wash·board 
(wŏshbôrd′, wôsh-)
(wŏshbôrd′, wôsh-)n.
1.
a. A board having a corrugated surface on which clothes can be rubbed in the process of laundering.
b. Music A similar board used as a percussion instrument.
2. A board fastened to a wall at the floor; a baseboard.
3. Nautical A thin plank fastened to the side of a boat or to the sill of a port to keep out the sea and the spray.
adj.
Having rows of ridges or indentations similar to those of a washboard: washboard abs; a washboard dirt road.