Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
effĭcācĭa, ae, f. [efficax], efficacy, efficiency, virtue (post-Aug.), Plin. 11, 5, 4, § 12; Amm. 14, 8, 5; 16, 12, 25; Vulg. Sirach, 9, 4; Lact. de Ira D. 10, 37.