noun

1. a band of electromagnetic radiation with wavelengths between gamma rays and ultraviolet radiation (c. .005 to c. 5 nanometers), produced by the bombardment of a substance (usually one of the heavy metals) by a stream of electrons moving at great velocity, as in a vacuum tube: X-rays are capable of penetrating opaque or solid substances, ionizing gases and body tissues through which they pass or, by extended exposure, destroying tissue, and affecting photographic plates and fluorescent screens: they are widely used in medicine for study, diagnosis, and treatment of certain organic disorders, esp. of internal structures of the body: usually used in pl.
2. a photograph made by means of X-rays

Etymology: transl. of Ger x-strahl (< x, algebraic symbol for an unknown quantity + strahl, ray): so named by Wilhelm Konrad Roentgen (1895), because of its unknown character

adjective

transitive verb