nuclear

American  

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

adjective

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.

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noun

Informal.

1. nuclear energy.

   switching to nuclear as a power source.

nuclear British  

/ ˈnjuːklɪə /

adjective

1. of, concerned with, or involving the nucleus of an atom

   nuclear fission

2. biology of, relating to, or contained within the nucleus of a cell

   a 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 nuclei

   a nuclear weapon

5. involving, concerned with, or possessing nuclear weapons

   nuclear war

   a nuclear strike

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nuclear Scientific  

/ no̅o̅′klē-ər /

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.

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Pronunciation

In pronouncing nuclear, the second and third syllables are most commonly said as , 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 . Since , the common pronunciation of ‑cle·ar, might also be represented, broadly, as , the pronunciation can be seen as coming from a process of metathesis, in which the and the 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.

Other Word Forms

• internuclear adjective
• multinuclear adjective
• postnuclear adjective

Etymology

Origin of nuclear

1840–50; nucle(us) + -ar ¹; compare French nucléaire

Explanation

Nuclear describes something that has to do with the nucleus — the central part — of an atom. If you're a nuclear physicist, you do a lot of work with that part of the atom. Nuclear power, which comes from nuclear fission — the energy released when the nucleus of an atom is split — is a controversial source of renewable energy. The word nuclear is sometimes used broadly to refer to the core of something. Your nuclear family is you, your parents, and your siblings — in a sense, the central part of your world, kind of like the nucleus of an atom.

Example Sentences

Missing nuclear official becomes 10th tied to U.S. secrets.

From MarketWatch • Apr. 15, 2026

Russia has never helped NPT nonweapons states make nuclear fuel; it sells them Russian enriched fuel and offers to take back their plutonium-laden spent fuel.

From The Wall Street Journal • Apr. 14, 2026

Cameco owns a 49% stake in nuclear reactor builder Westinghouse, giving it SMR exposure.

From Barron's • Apr. 14, 2026

Iran does not have nuclear weapons, and the UK government has said there is "no assessment" that Iran was trying to target Europe with missiles.

From BBC • Apr. 14, 2026

In Japan, a law set the maximum exposure allowed for a nuclear power plant worker under normal conditions at 50 mSv a year, or 100 mSv over five years.

From "Meltdown" by Deirdre Langeland

Related Words

• basic
• essential
• fundamental
• important
• key
• paramount
• pivotal
• significant