† phyˈlacticObs.rare. [ad.Gr. ϕυλακτικός adj., having the quality of guarding, f. stem ϕυλακ- (seeprec.).] A preservative; a prophylactic. 1706Cary (title) A Physician's Phylactic, Against a Lawyer's Venefic: or, An Answer to a Book, abusively Entitled, The Rights of the Christian Church, Asserted.