The quality of being efficacious; power or capacity to produce the intended effect or result.
Variant or alternative form of efficacy, combining Latin efficax (effective) with the -ity suffix (similar to -ness). This form is essentially obsolete, replaced by the simpler 'efficacy.'
This is a 'ghost word'—English speakers invented it logically (from efficacious + -ity) but then decided 'efficacy' was better, so 'efficacity' barely appears in real texts!
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