Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from The Century Dictionary.

  • Afraid; frightened.
  • A Middle English form of rath.
  • A Middle English preterit of ride.
  • An obsolete preterit of read.
  • noun A radical.
  • noun 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 the GNU version of the Collaborative International Dictionary of English.

  • noun 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 Wiktionary, Creative Commons Attribution/Share-Alike License.

  • adjective slang Excellent, short for radical.
  • noun metrology A non-SI unit of absorbed dose of radiation, equal to 0.01 gray.
  • noun Abbreviation of radian.
  • noun automotive, plumbing, slang Abbreviation of radiator.

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

  • noun a unit of absorbed ionizing radiation equal to 100 ergs per gram of irradiated material
  • noun 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)

Etymologies

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

[r(adiation) a(bsorbed) d(ose).]

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

[Short for radical.]

Examples

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