To inoculate a person or animal is to introduce immunologically active material (such as an antibody or antigen) into them especially in order to treat or prevent a disease. Inoculate can also mean "to introduce (something, such as a microorganism) into a suitable situation for growth," and in figurative use, it can mean "to protect as if by inoculation" or "to introduce something into the mind of."

// In 1796, the English physician Edward Jenner discovered that inoculating people with cowpox could provide immunity against smallpox.

// The cheese is inoculated with a starter culture to promote fermentation.

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"Truffle farmers ... inoculate oak or hazelnut seedlings with truffle spores, plant the seedlings and wait patiently often a decade or more for the underground relationship to mature. The eventual harvest is a reward for years of cooperation between tree and fungus." — David Shubin, The Weekly Calistogan (Calistoga, California), 30 Oct. 2025

If you think you see a connection between inoculate and ocular ("of or relating to the eye"), you have a good eye—both words look back to oculus, the Latin word for "eye." But what does the eye have to do with inoculation? Our answer lies in the original use of inoculate in Middle English: "to insert a bud into a plant for propagation." The Latin oculus was sometimes applied to things that were seen to resemble eyes, and one such thing was the bud of a plant. Inoculate was later applied to other forms of engrafting or implanting, including the introduction of vaccines as a preventative against disease.