1. a large membrane-bound compartment, found in the cells of nonbacterial organisms, that contains the bulk of the cell’s genetic material in the form of chromosomes.

2. in the central nervous system, a mass of cell bodies belonging to neurons with the same or related functions. Examples are the amygdaloid nuclei (see amygdala), the basal nuclei (see basal ganglia), the thalamic nuclei (see thalamus), and the nucleus accumbens. Compare ganglion.