X-ray
<B>1.</B> High-energy radiation with waves shorter than those of visible light.
X-rays possess the properties of penetrating most substances (to varying extents), of acting on a photographic film or plate (permitting radiography), and of causing a fluorescent screen to give off light (permitting fluoroscopy).
In low doses X-rays are used for making images that help to diagnose disease, and in high doses to treat cancer.
Formerly called a Roentgen ray.
<B>2.</B> An image obtained by means of X-rays