/ ˌprɒfɪˈlæktɪk; NAmE ˌprɑːf-/ adjective , noun
■ adjective
( medical ) done or used in order to prevent a disease :
prophylactic treatment
► prophy·lac·tic·al·ly / -kli; NAmE / adverb
■ noun
1.
( medical ) a medicine, device or course of action that prevents disease
2.
( NAmE , formal ) = condom
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WORD ORIGIN
late 16th cent.: from French prophylactique , from Greek prophulaktikos , from pro before + phulassein to guard.