vaccine

The noun probably comes partly from the English adjective vaccine, itself a learned borrowing from Latin vaccīnus, meaning "of or derived from a cow," from vacca ("cow"). It's also borrowed from French vaccine/vaccin, referring to cowpox material used to protect against smallpox — a coinage tied to physician Edward Jenner's work with cowpox as protection against smallpox.

The word began narrowly, describing cowpox itself and the material taken from it to guard against smallpox. From that specific, cattle-derived substance, it broadened into the general term for any preparation that trains the body's defenses against disease.

Cognates like Italian vaccina, Portuguese vacina, and Spanish vacuna all trace back to the same Latin root, showing how widely Jenner's cowpox-based idea spread across languages.