Definitions

1. noun

Either of the two nuclei that combine to form a zygote during fertilization; the male and female nuclei before they fuse.

“The pronucleus of the sperm and egg merged to form a zygote.”

2. noun

Either of the two haploid nuclei that form in the fertilized ovum before they fuse, or either of the two nuclei that form in the first cell division of the fertilized ovum.

“The pronucleus of the embryo began to divide into two distinct nuclei.”