| 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. |
| raffish |
carelessly unconventional or disreputable, sometimes appealingly so. [2 definitions] |
| raffle |
a type of lottery in which participants buy tickets, one of which is drawn to determine the prizewinner. [2 definitions] |
| raft1 |
a flat platform made of buoyant materials such as wood or air-filled barrels, designed to float and often to support or carry people or goods. [6 definitions] |
| raft2 |
(informal) very many; a large quantity. |
| rafter |
one of the usu. sloping timbers that support the covering material of a roof. |