rip·rap I. \ˈriˌprap\noun Etymology: from obsolete riprap sound of rapping, reduplication of rap (I) 1.: a foundation or sustaining wall of stones thrown together without order (as in deep water, on a soft bottom, or on an embankment slope to prevent erosion) 2.: stone used for riprap II. transitive verb : to form a riprap in or upon : strengthen or support with a riprap < raprapped the breakwater with stone >