[ noo-klee-er, nyoo- or, by metathesis, -kyuh-ler ]
/ ˈnu kli ər, ˈnyu- or, by metathesis, -kyə lər /


pertaining to or involving atomic weapons: nuclear war.
operated or powered by atomic energy: a nuclear submarine.
(of a nation or group of nations) having atomic weapons.
of, relating to, or forming a nucleus.
of, relating to, or like the nuclear family: nuclear bonds.

noun Informal.

nuclear energy: switching to nuclear as a power source.



We’ve gathered some interesting words donated to English from Portuguese … as well as some that just don’t translate at all. Do you know what they mean?
Question 1 of 11
Which of the following animal names traces its immediate origin to Portuguese?

Origin of nuclear

1840–50; nucle(us) + -ar1; compare French nucléaire

pronunciation note for nuclear

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.


in·ter·nu·cle·ar, adjectivemul·ti·nu·cle·ar, adjectivepost·nu·cle·ar, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

Example sentences from the Web for nuclear

British Dictionary definitions for nuclear

/ (ˈnjuːklɪə) /


of, concerned with, or involving the nucleus of an atomnuclear fission
biology of, relating to, or contained within the nucleus of a cella nuclear membrane
of, relating to, forming, or resembling any other kind of nucleus
of, concerned with, or operated by energy from fission or fusion of atomic nucleia nuclear weapon
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

Medical definitions for nuclear

[ nōōklē-ər ]


Of or forming a nucleus.
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.

Scientific definitions for nuclear

[ nōōklē-ər ]

Relating to or forming a cell nucleus.
Relating to atomic nuclei.
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.