Real Dictionary

Roentgen in American English
a basic unit of exposure to X-rays, gamma rays, or other ionizing radiation, equal to the amount of radiation that will produce an electric charge of 0.000258 coulomb per kilogram of dry air
Wilˌ helmˈ Konˌ rad (ˈvɪlˌhɛlmˈkɔnˌʀɑt) 1845-1923; Ger. physicist: discoverer of X-rays
noun: a unit of exposure dose that measures x-rays or gamma rays in terms of the ions or electrons produced in dry air at 0° C and one atmosphere, equal to the amount of radiation producing one electrostatic unit of positive or negative charge per cubic centime

Roentgen in British English
noun: a unit of dose of electromagnetic radiation equal to the dose that will produce in air a charge of 0.258 × 10–3 coulomb on all ions of one sign, when all the electrons of both signs liberated in a volume of air of mass one kilogram are stopped completely
noun: Wilhelm Konrad (ˈvɪlhɛlm ˈkɔnraːt ). 1845–1923, German physicist, who in 1895 discovered X-rays: Nobel prize for physics 1901