from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A unit of energy absorbed from ionizing radiation, equal to 100 ergs per gram or 0.01 joules per kilogram of irradiated material. It has been replaced as a standard scientific unit by the gray.
  • adj. Slang Excellent; wonderful.
  • abbr. radian

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • adj. Excellent, short for radical.
  • n. A non-SI unit of absorbed dose of radiation, equal to 0.01 gray.
  • n. Abbreviation of radian.
  • n. Abbreviation of radiator.

from the GNU version of the Collaborative International Dictionary of English

  • n. a unit of measurement of the amount of ionizing radiation absorbed by an object, equal to an energy of 100 ergs per gram of irradiated material (equal to 0.01 gray).
  • imp. & p. p. of read, rede.

from The Century Dictionary and Cyclopedia

  • Afraid; frightened.
  • A Middle English form of rath.
  • A Middle English preterit of ride.
  • An obsolete preterit of read.
  • n. A radical.
  • n. In photometry, a proposed unit of quantity of light equal to the amount of energy in luminous form obtained in one second from a light-flux of one lumen. The rad is of a lumen-hour.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a unit of absorbed ionizing radiation equal to 100 ergs per gram of irradiated material
  • n. the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees)


r(adiation) a(bsorbed) d(ose).
Short for radical.
(American Heritage® Dictionary of the English Language, Fourth Edition)



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