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Definition of nucleus:

  1. A body, usually spheroidal, in a cell or a protozoan, distinguished from the surrounding protoplasm by a difference in refrangibility and in behavior towards chemical reagents. It is more or less protoplasmic, and consists of a clear fluid ( achromatin) through which extends a network of fibers ( chromatin) in which may be suspended a second rounded body, the nucleolus ( see Nucleoplasm). See Cell division, under Division.
  2. A kernel; hence, a central mass or point about which matter is gathered, or to which accretion is made; the central or material portion; - used both literally and figuratively.
  3. A visceral mass, containing the stomach and other organs, in Tunicata and some mollusks.
  4. A whole seed, as contained within the seed coats.
  5. An incipient ovule of soft cellular tissue.
  6. The body or the head of a comet.
  7. The central part around which additional growths are added, as of an operculum.
  8. The tip, or earliest part, of a univalve or bivalve shell.


nitty-gritty, matter, embryo, core group, spark, magnetic core, heart and soul, foundation, bud, burden, germ, substance, premise, pith, effect, cell nucleus, inwardness, karyon, basis, lens nucleus, sum, start, gist, centre, core.

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