| radiosensitive |
sensitive or susceptible to destruction by radiant energy, as living organisms or tissue. |
| radiosonde |
an airborne meteorological instrument that radios information about air temperature, pressure, and humidity to ground stations; radiometeorograph. |
| radio spectrum |
the portion of the electromagnetic spectrum consisting of radio waves, esp. those most frequently used in radio and television broadcasting, from ten kilohertz to 300 gigahertz. |
| radio station |
an organization equipped for broadcasting radio. [2 definitions] |
| radiotelegraph |
a telegraph in which signals are transmitted by radio rather than by wires. |
| radiotelegraphy |
the design, construction, or operation of telegraphs whose signals are transmitted by radio waves. |
| radiotelephone |
a telephone whose sound is transmitted by radio waves; radiophone. |
| radio telescope |
a concave reflector or array of reflectors designed to collect and focus extraterrestrial radio waves for analysis. |
| radiotherapy |
the treatment of an illness with radioactive substances or x-rays. |
| radio wave |
an electromagnetic wave with a wavelength of between one millimeter and thirty thousand meters, or a frequency of between ten kilohertz and three hundred thousand megahertz. |
| radish |
one of a group of herbs of the cabbage family that have a pungently flavored, crisp, edible root. [2 definitions] |
| radium |
a radioactive chemical element that has eighty-eight protons in each nucleus and that occurs in pure form as a solid metal, used esp. as a radiation source for cancer treatment. (symbol: Ra) |
| radium therapy |
the treatment of disease, esp. cancer, by means of radium. |
| radius |
a straight line segment extending from the center to the surface of a sphere or from the center to the circumference of a circle. [7 definitions] |
| radius vector |
a straight line that joins the origin of a vector, at the intersection of two coordinates, to a given point on the same plane. [2 definitions] |
| radome |
a dome-shaped structure that protects a radar antenna from the weather, esp. on aircraft, without affecting reception. |
| radon |
a radioactive chemical element of the inert gas group that has eighty-six protons in each nucleus and that is produced by the radioactive decay of trace amounts of radium in the soil. (symbol: Rn) |
| radula |
in mollusks, a ribbonlike structure in the mouth that bears many rows of teeth. |
| RAF |
abbreviation of "Royal Air Force." |
| raffia |
a type of palm native to Madagascar, or the fiber harvested from its leafstalks, used for rope, basketweaving, and the like. [2 definitions] |
| raffinose |
a white crystalline sugar obtained from the sugar beet, cottonseed, and the like. |