1 [count] : a small, fancy object that is put on something else to make it more attractive
She wore a hair ornament.
(US) the hood ornament on a car [=a small metal figure on the front edge of a car's hood]
Christmas ornaments [=small balls, figures, etc., that are hung on a Christmas tree for decoration]
2 [noncount] formal : a way to make something look more attractive and less plain
A satin bow was used for ornament. [=decoration]
The columns are there purely as ornament—they have no structural function.