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.

The body or the head of a comet.

An incipient ovule of soft cellular tissue.

A whole seed, as contained within the seed coats.

is inserted into a pearl-producing oyster to speed up the pearl growing process. The nuclei act as the irritant upon which nacre is deposited, and are usually made from the shell of North American freshwater mussels.

the center around which things are formed.Ý Beads made from the shell of freshwater mussels are used as the center around which oysters lay nacre to form a cultured pearl

Usually, a small rounded piece of shell from an American freshwater mussel. For freshwater pearl cultivation, the nucleus usually is a shaped piece of mantle from another freshwater mussel.

The irritant imbedded in a mollusk to force production of nacre.

The solid chunk of ice and dust in the head of a comet.

The actual solid body of a comet. The nucleus is rarely visible when the comet is in the inner solar system because of the coma. It has been referred to as a "dirty snowball" because it is believed to be composed of about 75 percent of various ices and about 25 percent of various dusts. A photo of the nucleus of Halley's comet by the Giotto probe revealed the nucleus as an asteroidal-looking body. Most comet's have a nucleus that measures only a few kilometers across.

(astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail

is the solid part which contains almost all of the mass of a comet. The nucleus is made up of a conglomerate of rocky fragments and ices of methane, ammonia, carbon dioxide, water, and other substances. The nucleus of a comet is typically a few kilometers in diameter.

the center or most important point of an object

(nucleus pulposus): soft gel-like center of an intervertebral disc.

The soft center of a spinal disk.

a small colony of four to six combs, with a fertile queen, workers, possibly some drones, and some brood and, stores

a hive of bees which consists of fewer frames than a typical hive and may be smaller in size. A nucleus usually consists of two to five frames of comb and used primarily for starting new colonies or rearing or storing queens; also called and commonly referred to a nuc.

a small hive of bees, usually covering from two to five frames of comb and used primarily for starting new colonies, rear ing or storing queens; also called "nuc."