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radiate to send out rays, as of heat or electromagnetic radiation. [7 definitions]
radiation the emission of particles or waves of energy, as by radioactive material or by electrical circuits or devices. [3 definitions]
radiationless combined form of radiation.
radiation sickness sickness induced by overexposure to ionizing radiation such as x-rays or gamma rays, resulting in nausea, diarrhea, bleeding, hair loss, sterility, and often death.
radiator a device, such as that in a car, consisting of tubes through which fluid coolant passes. [3 definitions]
radical of or relating to roots, origins, or fundamental characteristics; basic. [6 definitions]
radicalism the advocacy of radical political or social changes. [2 definitions]
radicalize to make or become radical, esp. in political or social ideas.
radical sign a mathematical sign placed before a quantity to indicate extraction of its root.
radicand in mathematics, the number, variable, or quantity under a radical sign.
radicchio a variety of chicory with slightly bitter, purplish red leaves that are used in salads.
radicle the lower part of a plant embryo or seedling, esp. the beginnings of a root.
radii a pl. of radius.
radio the sending of communications by means of electromagnetic waves in the frequency range from ten kilocycles to three hundred thousand megacycles. [9 definitions]
radio- radio. [3 definitions]
radioactive emitting energy or subatomic particles as a result of the decay of unstable isotopes. [2 definitions]
radioactive dating any of several methods of determining the age of an artifact, rock, or bone based on the known rate of decay of radioactive isotopes.
radioactivity the emission or amount of emission of energy or subatomic particles by the nuclei of certain unstable isotopes of elements as they decay.
radio astronomy the study of the universe by observation and analysis of extraterrestrial radio waves.
radio beacon a stationary source of radio waves that emits a distinctive signal as a navigational aid for ships and aircraft.
radiobiology the branch of biology concerned with the effects of radiation on living tissue and the use of radioactive tracers in the study of biological processes.