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rad

1 American  
[rad] / ræd /

noun

Physics.

  1. a unit of absorbed dose of radiation equal to 0.01 gray: not a standard SI unit, the rad is still used, especially in the U.S., but it is increasingly disfavored.

rad 2 American  
[rad] / ræd /

noun

  1. Informal. a radical, especially a person with extreme views on political and social issues.

adjective

radder, raddest

  1. Slang. excellent; wonderful; cool.

    a high speed, high energy, totally rad racing game.
rad 3 American  
[rad] / ræd /

abbreviation

Mathematics.

  1. radian; radians.

rad. 4 American  

abbreviation

Mathematics.

  1. radical.

  2. radix.

rad. 1 British  

abbreviation

  1. radical

  2. radius

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
rad 2 British  
/ ræd /

noun

  1. a former unit of absorbed ionizing radiation dose equivalent to an energy absorption per unit mass of 0.01 joule per kilogram of irradiated material. 1 rad is equivalent to 0.01 gray

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
rad 3 British  

symbol

  1. radian

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
rad Scientific  
/ răd /

  1. A unit used to measure energy absorbed by a material from radiation. One rad is equal to 100 ergs per gram of material. Many scientists now measure this energy in grays rather than in rads.

rad Cultural  

  1. An acronym for r adiation a bsorbed d ose. A unit of energy absorbed from ionizing radiation.

Etymology

Origin of rad1

First recorded in 1915–20; r(adiation) a(bsorbed) d(ose)

Origin of rad2

First recorded in 1820–25 rad 2 for 1; 1975–80 rad 2 for 2; shortening of radical

Origin of rad3

First recorded in 1910–15; shortening

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Also: How Liquid Death made water rad as hell, and the uncertain fate of TikTok in America.

From Slate • Mar. 16, 2024

Madisynn drops into our lives by way of a "diff dimensh" otherwise known as a hellscape, which she navigates like any other rad party, or her hometown of Fort Lauderdale.

From Salon • Dec. 26, 2022

At the end of the day, none of that has to do with how rad you are as a 10-year-old.

From Seattle Times • Nov. 3, 2022

“That makes this a rad time to do this job, even with whatever is going on in the world.”

From Los Angeles Times • Oct. 11, 2022

I’m not going to hop in unless there’s something really rad.

From "Free Lunch" by Rex Ogle

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.