(medicine) Prevention of, or protective treatment for, disease. / (chess) A move or strategy that frustrates an opponent's plan or tactic.

plural of prophylaxy

Archaic form of prophylaxis.

(medicine) A form of prevention, usually medication, taken after exposure (or probable exposure) to a pathogen, preventing development of disease after such exposure; especially, as against HIV.

(medicine) A form of prevention, usually medication, that is taken before exposure to a pathogen, preventing development of disease after such exposure. Especially: