a precious stone of convex hemispherical or oval form, polished but not cut into facets.
2.
an ornamental motif resembling this, either concave or convex and often surrounded by ornately carved leaf patterns, used on furniture of the 18th century.
1570s, from Fr. cabochon (14c.), augmentative of caboche (12c.), augmentative or pejorative formation, ultimately from L. caput "head." Essentially the same word as cabbage.