(physics) A nucleus of an atom; consisting of protons and neutrons, surrounded by an electron cloud.

(uncommon) Nuclear winter.

(physics) an early nuclear reactor fuelled by uranium and moderated with graphite

(physics, chemistry) the equivalent of an atom in which either the nucleus, or an electron, is replaced by some other subatomic particle

(physics) a hydrogen-like system consisting of an ordinary nucleus with a hadron in orbit.

The era, starting in the mid-1940s, during which nuclear energy was developed, and in which it was thought that all energy would be provided by such sources.

(physics) any device that converts the energy of particles emitted from atomic nuclei into electrical energy

(physics, chemistry) Any atom which has a single valence electron in a shell well outside any other electrons in the aton; approximates the hydrogen atom.

An extremely accurate reference clock whose operation is based on an atomic process, typically the frequency of electromagnetic radiation associated with a specified energy-level transition in an element such as cesium.

A nuclear weapon.