wash·board / ˈwäshˌbôrd; ˈwôsh-/ • n. 1. a board made of ridged wood or a sheet of corrugated zinc, used when washing clothes as a surface against which to scrub them. ∎ a similar board played as a percussion instrument by scraping. ∎ the surface of a worn, uneven road. ∎ [as adj.] denoting a man's stomach that is lean and has well-defined muscles.2. a board fixed along the side of a boat to prevent water from spilling in over the edge.• v. [tr.] [usu. as adj.] (washboarded) cause ridges to develop in (a road or road surface): a road left washboarded by winter frost.