fertilization

n. impregnation, insemination; act of enriching the soil by the addition of organic or chemical substances (also fertilisation)

Fertilization (also known as conception, fecundation and syngamy), is fusion of gametes to form a new organism of the same species. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization.
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Fertilization /fer·ti·li·za·tion/ impregnation ; union of male and female gametes to form the diploid zygote, leading to development of a new [more]Fertilization - Community and Resources

Noun
1. creation by the physical union of male and female gametes; of sperm and ova in an animal or pollen and ovule in a plant
(synonym) fertilisation, fecundation, impregnation
(hypernym) creation, conception
(hyponym) pollination, pollenation
(derivation) inseminate, fecundate, fertilize, fertilise
2. making fertile as by applying fertilizer or manure
(synonym) fertilisation, fecundation, dressing
(hypernym) enrichment
(hyponym) top dressing
(derivation) fertilize, fertilise, feed

Fertilization is the process of combining the male gamete, or "sperm," with the female gamete, or "ovum." The product of this combination is a cell called a zygote.