To make (soil or land) more fertile or productive by adding suitable substances to it. Farmers often fertilize their fields in the spring to ensure a good harvest.
To cause (an egg, female animal, or plant) to develop a new individual by introducing male reproductive material. The biologist fertilized the eggs in the laboratory to study the development process.
To enrich or stimulate (the mind, environment, etc.) so that it becomes more productive or creative. Reading widely can fertilize a writer's imagination.