A round, convex molding. See Illust.
. [1913 Webster
" In Roman work it is usually a quarter circle in section; in Greek work it is flatter, and is equivalent to the echinus; that is, it has in section the elastic curve of the shell of the sea urchin. In mediæval architecture it is not distinguishable from the multitude of convex moldings, of all sections, which are used."