Definition of efficacious adjective from the Oxford Advanced American Dictionary

     

    efficacious

     adjective
    adjective
    NAmE//ˌɛfəˈkeɪʃəs//
     
    (formal)
     
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  1. 1(of things, not of people) producing the result that was wanted or intended synonym effective
  2. 2 They hope the new drug will prove especially efficacious in the relief of pain.
See the Oxford Advanced Learner's Dictionary entry: efficacious