noun in·ef·fi·ca·cy \(ˌ)i-ˈne-fi-kə-sē\

Definition of inefficacy

  1. :  lack of power to produce a desired effect

Origin and Etymology of inefficacy

Late Latin inefficacia, from Latin inefficac-, inefficax inefficacious, from in- + efficac-, efficax efficacious

First Known Use: circa 1615

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