allowing X-rays to pass through; appear as a dark area on a radiograph

Permitting the penetration of X-rays.

The black or dark areas in a radiograph that result from the ability of radiant energy to pass through the structure. Less dense structures (e.g., the pulp) are radiolucent.

a stone such as a uric acid stone is radiolucent, meaning it does not cast a shadow on plain x-rays

an object/item/mass that appears on a radiograph that allows the x-ray to pass through it when in normal circumstances it would not. (eg., a bone that does not look as dense as the bones around it.