prophylactic /pɹɒfəˈlæktɪk/noun 3adjective 1forms 3 noun3 •A medicine which preserves or defends against disease; a preventive. •(US, euphemistic) A prophylactic condom.It is not clear whether such education is to be directed to homosexuals (for whom prophylactics are not a contraceptive) or to heterosexuals as well (for whom prophylactics are a contraceptive). — 1977 •(figurative) Any device or mechanism intended to prevent harmful consequences.The securities laws are a prophylactic against stock fraud. adjective1 •Serving to prevent or protect against an undesired effect, especially disease or pregnancy. formsprophylactics · more prophylactic · most prophylactic