I. pro ‧ phy ‧ lac ‧ tic 1 /ˌprɒfəˈlæktɪk◂, ˌprɒfɪˈlæktɪk◂ $ ˌprɑː-/ BrE AmE adjective technical
[ Date: 1500-1600 ; Language: Greek ; Origin: prophylaktikos , from prophylassein 'to guard before' , from phylax 'guard' ]
intended to prevent disease:
prophylactic antibiotics
II. prophylactic 2 BrE AmE noun [countable]
1 . technical something used to prevent disease
2 . American English formal a ↑ condom – often used humorously