What part of speech is the word "prevent" as used in "a word or phrase which is nearest in meaning to Illness..........?"

The question asks for a word or phrase nearest in meaning to "Illness". However, none of the provided options (Advisable, Prevents, Boiled) are direct synonyms for "Illness".

Given the options and the likely context of health-related questions (as seen in previous questions about preventing germs and treating water), the word that is most functionally related to "Illness" among the choices is "Prevents". One often takes actions to prevent illness.

Therefore, the most appropriate option, considering a functional relationship rather than a direct synonym, is:

Prevents