To add nutrients to soil to help plants grow better, or (in biology) to combine male and female cells to create a new organism.
From Latin fertilis (fruitful) via Old French fertiliser. First used in agriculture in the 1600s, later extended to biological reproduction in the 1800s as science advanced.
Before the 1800s, no one had a special word for what happens when sperm meets egg—scientists literally borrowed the farming term, showing how agricultural knowledge shaped our understanding of life itself.
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