Nū'cle-ūs, n.

noun

n.; Eng. pl. NŪ'CLE-US-ES, Lat. pl. NŪ-CLE-I. [Lat., from nux, nucis, nut; It. & Sp. nucleo.] 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;—both literally and figuratively. It must contain, itself, a nucleus of truth. I. Taylor.

(Astron.) The central part of the body or the head of a comet.
(Bot.) The minute, pulpy rudiment of the seed; also, the whole body of the seed or the kernel.
(Histology.) A body, usually of a round or oval shape, found within cells, having generally separate chemical natural powers, and a higher refracting power than the other contents of the cell. By some it is regarded as maintaining the life of the cell, and as giving rise to new cells by its division; cytoblast.
(Zoöl.) The shell or shell-like process that hangs from the back of nucleobranchs, containing the digestive and respiratory organs.