Crossword Dictionary

What's The Definition Of Nucleus?

\Nu"cle*us\, n.; pl. E. {Nucleuses}, L. {Nuclei}. [L., a kernel, dim. fr. nux, nucis, nut. Cf. {Newel} post.] 1. 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. It must contain within itself a nucleus of truth. --I. Taylor. 2. (Astron.) The body or the head of a comet. 3. (Bot.) (a) An incipient ovule of soft cellular tissue. (b) A whole seed, as contained within the seed coats. 4. (Biol.) 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}. Note: The nucleus is sometimes termed the endoplast or endoblast, and in the protozoa is supposed to be concerned in the female part of the reproductive process. See {Karyokinesis}. 5. (Zo["o]l.) (a) The tip, or earliest part, of a univalve or bivalve shell. (b) The central part around which additional growths are added, as of an operculum. (c) A visceral mass, containing the stomach and other organs, in Tunicata and some mollusks.