slick·en·side I. \ˈslikənˌsīd\noun Etymology: English dialect slicken smooth (alteration of slick) (II) + side : a smooth striated polished surface produced on rock by movement along a fault, a subsidiary fracture, a bedding plane, or at the bottom of a landslide — usually used in plural < interpretation of the relative age of the faulting, on the basis of slickensides alone, is difficult — J.D.Forrester > II. transitive verb (-ed/-ing/-s) : to form slickensides upon