1.Definition: capable of preventing conception or impregnation

Related Adjective(s):antifertility, contraceptive

2.Definition: preventing or contributing to the prevention of disease

"Vaccines are prophylactic", "A prophylactic drug"

Related Adjective(s):preventative, preventive

3.Definition: warding off

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

Related Adjective(s):cautionary