a part of the cell containing DNA and RNA and responsible for growth and reproduction
"The nucleus acts as the control center of the cell, housing its genetic material to direct growth and reproduction."
the positively charged dense center of an atom
"The proton and neutron reside within the nucleus, which is the positively charged dense center of the atom."
a small group of indispensable persons or things
"five periodicals make up the core of their publishing program"
(astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail
"As the comet draws closer to the sun, its nucleus begins to vaporize, releasing clouds of gas and dust that create the spectacular tail."
any histologically identifiable mass of neural cell bodies in the brain or spinal cord
"The damaged nucleus caused paralysis because it contains a cluster of motor neuron cell bodies that control movement."
the central structure of the lens that is surrounded by the cortex
"The surgeon carefully removed the cloudy nucleus from inside the eye's natural lens during cataract surgery."
The core, central part of something, around which other elements are assembled.
"The nucleus of the atom is the dense core around which electrons orbit."
In plain English: The nucleus is the central part of an atom that contains protons and neutrons.
"The nucleus at the center of an atom contains most of its mass."
Usage: Use nucleus to refer specifically to the dense center or control point of an atom, cell, or organization where activity is concentrated. Avoid confusing it with "nucleus" as a verb form, since this word functions only as a noun in standard English.
The word nucleus comes from Latin, where it originally meant "kernel" or "core." Its earliest English uses described the head of a comet and the center of a seed, while the scientific term for an atom's central part was coined by Michael Faraday in 1844.