[ rey-dee-oh-ak-tiv ]
/ ˌreɪ di oʊˈæk tɪv /

adjective Physics, Chemistry.

of, pertaining to, exhibiting, or caused by radioactivity.

Nearby words

  1. radio-controlled,
  2. radio-telephone,
  3. radioacoustics,
  4. radioactinium,
  5. radioactivate,
  6. radioactive constant,
  7. radioactive dating,
  8. radioactive decay,
  9. radioactive fallout,
  10. radioactive iodine

Origin of radioactive

First recorded in 1895–1900; radio- + active

Related formsra·di·o·ac·tive·ly, adverbnon·ra·di·o·ac·tive, adjectiveun·ra·di·o·ac·tive, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for radioactive

British Dictionary definitions for radioactive


/ (ˌreɪdɪəʊˈæktɪv) /


exhibiting, using, or concerned with radioactivity
Derived Formsradioactively, adverb

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

Word Origin and History for radioactive



1898, from French radio-actif, coined by Pierre and Marie Curie from radio-, comb. form of Latin radius (see radiation) + actif "active" (see active).

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for radioactive


[ rā′dē-ō-ăktĭv ]


Of or exhibiting radioactivity.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Culture definitions for radioactive


A descriptive term for a material made up of atoms in which radioactivity occurs.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.