nuclear

UK: /ˈnjuːkliə^r/

US: /ˈnukliɚ, ˈnju-/

US: (no̅o̅′klē ər, nyo̅o̅′- or, by metathesis, -kyə lər)

WordReference Random House Learner's Dictionary of American English © 2025

nu•cle•ar /ˈnukliɚ, ˈnyu-/   adj. 

1. relating to or involving atomic weapons:
   a nuclear war.
2. Energy operated or powered by atomic energy:
   a nuclear power plant; a nuclear submarine.
3. of, relating to, or forming a nucleus:
   [before a noun] nuclear particles.

WordReference Random House Unabridged Dictionary of American English © 2025

nu•cle•ar  (no̅o̅′klē ər, nyo̅o̅′- or, by metathesis, -kyə lər), adj. 

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

n. Informal. 

6. Energy, Informal Terms nuclear energy:
   switching to nuclear as a power source.

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

Pronunciation

In pronouncing nuclear, the second and third syllables are most commonly said as (-klē 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 (-kyə lər). Since (-klē ər), the common pronunciation of -cle•ar, might also be represented, broadly, as (-klə yər), the (-kyə lər) pronunciation can be seen as coming from a process of metathesis, in which the (l) and the (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.

Collins Concise English Dictionary © HarperCollins Publishers::

nuclear / ˈnjuːklɪə/ adjective

1. of, concerned with, or involving the nucleus of an atom: nuclear fission
2. 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