roentgeno-, roentgen- +
(German: radiation, "x-ray"; X-ray; 1896, translation of German X-strahl, from X, "algebraic symbol for an unknown quantity", + Strahl, "beam, ray")
So called after its discoverer, a German physicist, Wilhelm Konrad Roentgen [1845-1923], who discovered roentgen rays [x-rays] in 1895; winner of the Nobel prize in physics in 1901.
Related "roentgen, x-ray" units: Roentgen Biography; Chemical Element: roentgenium.