ˈeksˌrā also ˈ ̷ ̷ˈ ̷ ̷ noun
Usage: usually capitalized X
Etymology: x (I) ; translation of German x-strahl
1. : any of the electromagnetic radiations having the nature of visible light but a wavelength approximately between 0.1 and 100 angstroms that is usually produced by bombarding a metallic target with fast electrons in vacuum so that the spectrum of the radiation emitted consists of lines characteristic of the target material and that has the properties of ionizing a gas upon passage through it, of penetrating through various thicknesses of all solids, of producing secondary radiations by impinging on material bodies, and of acting on photographic films and plates and on fluorescent screens : a photon or a stream of photons produced by excitation of an atom by impact of a fast moving electron
2. : a photograph obtained by the use of X rays