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

  • imp. & p. p. of read, rede.
  • 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).

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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