Definition of "Prophylactic" :

noun: contraceptive device consisting of a sheath of thin rubber or latex that is worn over the penis during intercourse

noun: remedy that prevents or slows the course of an illness or disease

adjective: preventing or contributing to the prevention of disease

"Vaccines are prophylactic."

adjective: warding off

"The swastika...a very ancient prophylactic symbol occurring among all peoples."

adjective: capable of preventing conception or impregnation