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From The Collaborative International Dictionary of English v.0.48:
Nucleolus \Nu*cle"o*lus\, n.; pl. Nucleoli. [L., a little nut, dim. of nucleus.] 1. A little nucleus. [1913 Webster] 2. (Biol.) A small rounded body contained in the nucleus of a cell or a protozoan. [1913 Webster] Note: It was termed by Agassiz the entoblast. In the protozoa, where it may be situated on one side of the nucleus, it is sometimes called the endoplastule, and is supposed to be concerned in the male part of the reproductive process. See Nucleus. [1913 Webster]