mid-15c., "implant a bud into a plant," from Latin inoculatus, past participle of inoculare "graft in, implant," from in- "in" (see in-(2)) + oculus "bud," originally "eye" (see eye, n.). Meaning "implant germs of a disease to produce immunity" first recorded (in inoculation) 1714, originally in reference to smallpox. After 1799, often used in sense of "to vaccine inoculate." Related: Inoculated; inoculating.