Definition of nucleus

• n. - 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.
• n. - The body or the head of a comet.
• n. - An incipient ovule of soft cellular tissue.
• n. - A whole seed, as contained within the seed coats.
• n. - 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.
• n. - The tip, or earliest part, of a univalve or bivalve shell.
• n. - The central part around which additional growths are added, as of an operculum.
• n. - A visceral mass, containing the stomach and other organs, in Tunicata and some mollusks.