[noo-klee-er, nyoo- or, by metathesis, -kyuh-ler]
  1. pertaining to or involving atomic weapons: nuclear war.
  2. operated or powered by atomic energy: a nuclear submarine.
  3. (of a nation or group of nations) having atomic weapons.
  4. of, relating to, or forming a nucleus.
  5. of, relating to, or like the nuclear family: nuclear bonds.
noun Informal.
  1. nuclear energy: switching to nuclear as a power source.

Origin of nuclear

1840–50; nucle(us) + -ar1; compare French nucléaire
Related formsin·ter·nu·cle·ar, adjectivemul·ti·nu·cle·ar, adjectivepost·nu·cle·ar, adjective

Pronunciation note

In pronouncing nuclear, the second and third syllables are most commonly said as [-klee-er] /-kli ər/, a sequence of sounds that directly reflects the spelled sequence ‐cle · ar. In recent years, a somewhat controversial pronunciation has come to public attention, with these two final syllables said as [-kyuh-ler] /-kyə lər/. Since [-klee-er] /-kli ər/, the common pronunciation of ‐cle · ar, might also be represented, broadly, as [-kluh-yer] /-klə yər/, the [-kyuh-ler] /-kyə lər/ pronunciation can be seen as coming from a process of metathesis, in which the [l] /l/ and the [y] /y/ change places. The resulting pronunciation is reinforced by analogy with such words as molecular, particular, and muscular, and although it occurs with some frequency among highly educated speakers, including scientists, professors, and government officials, it is disapproved of by many. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for internuclear


  1. of, concerned with, or involving the nucleus of an atomnuclear fission
  2. biology of, relating to, or contained within the nucleus of a cella nuclear membrane
  3. of, relating to, forming, or resembling any other kind of nucleus
  4. of, concerned with, or operated by energy from fission or fusion of atomic nucleia nuclear weapon
  5. involving, concerned with, or possessing nuclear weaponsnuclear war; a nuclear strike
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 internuclear



1846, "of or like the nucleus of a cell," from nucleus + -ar, probably by influence of French nucléaire. Use in atomic physics is from 1914; of weapons, from 1945. Hence nuclear physics (1933), nuclear energy (1941), nuclear war (1954). Nuclear winter coined by Richard Turco, but first attested in article by Carl Sagan in "Parade" magazine, Oct. 30, 1983. General sense of "central" is from 1912. Nuclear family, originally a sociologists' term, is first attested 1949 in "Social Structure," by American anthropologist G.P. Murdock (1897-1985). Alternative adjective nucleal is recorded from 1840.

Online Etymology Dictionary, © 2010 Douglas Harper

internuclear in Medicine


  1. Located or occurring between nuclei.
  2. Located between nerve cell groups in the brain or retina.


  1. Of or forming a nucleus.
  2. Of or relating to atomic nuclei.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

internuclear in Science


  1. Relating to or forming a cell nucleus.
  2. Relating to atomic nuclei.
  3. Using energy derived from the nuclei of atoms through fission or fusion reactions.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.