Dictionary.com
Thesaurus.com
Synonyms

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  
/ 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. 2 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 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.

Hahn: This woman had been working with Marvel and “Agatha,” and so she was kind of sent my way, and then I kept working with her, and she’s rad.

From Los Angeles Times • Jun. 5, 2025

“We believe in respect, kindness, and love. We are huge fans of other women-owned companies, LGBTQIA+ communities, and rad men’s companies too. None of that feels political to us,” she said.

From Slate • Jul. 23, 2024

Here are three potential itineraries for three different kinds of rad dads: those who love the great outdoors, fall head over heels for food and dig the arts.

From Seattle Times • Jun. 1, 2024

I feel like I never imagined a year in my career where I would get to work more than I am not working, and that's happening, and that's pretty rad.

From Salon • Jun. 4, 2023

I hoped to grow up to be at least half as rad as her.

From "The First Rule of Punk" by Celia C. Pérez

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.