Explanation:

- The word 'Vaccine' comes from the Latin word "vacca," which means ‘cow’.

- This is because Edward Jenner used material from cowpox (a disease found in cows) to create the first smallpox vaccine.

- Option 1: Antibody – This is not the origin. Antibodies are proteins produced by the body in response to a vaccine.

- Option 2: Immunity – This refers to the body's ability to resist infection, but is not the Latin root of 'vaccine'.

- Option 3: Cow – Correct Answer. 'Vacca' is Latin for cow, directly linked to the term 'vaccine'.

- Option 4: Guinea pig – Although guinea pigs are used in experiments, they have no relation to the word's Latin origin.