noun the body or the head of a comet.
2. nucleus ·noun an incipient ovule of soft cellular tissue.
3. nucleus ·noun a whole seed, as contained within the seed coats.
4. nucleus ·noun the tip, or earliest part, of a univalve or bivalve shell.
5. nucleus ·noun a visceral mass, containing the stomach and other organs, in tunicata and some mollusks.
6. nucleus ·noun the central part around which additional growths are added, as of an operculum.
7. nucleus ·noun 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.
8. nucleus ·noun 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.