'smooth-edged' originates from the combination of 'smooth' and 'edge', where 'smooth' meant 'even or without roughness' and 'edge' referred to 'the boundary or outer surface'.

'smooth' and 'edge' have been used in English since the Middle Ages, and their combination into 'smooth-edged' reflects the natural evolution of descriptive language.

Initially, 'smooth' and 'edge' were used separately to describe surfaces and boundaries, but their combination into 'smooth-edged' specifically describes an even boundary.