Source : Webster's Revised Unabridged Dictionary (1913)

Prophylaxis \Proph`y*lax"is\, n. [NL. See {Prophylactic}.]
   (Med.)
   The art of preserving from, or of preventing, disease; the
   observance of the rules necessary for the preservation of
   health; preservative or preventive treatment.

Source : WordNet®

prophylaxis
     n : the prevention of disease