Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
effĭcācĭter, adv., efficaciously, effectually, v. efficax fin.
effĭcax, ācis, adj. [efficio], efficacious, effectual, powerful, efficient (mostly postAug.; not in Cic. and Caes; but cf. efficacitas): nosti Marcellum, quam tardus et parum efficax sit, Cael. ap. Cic. Fam. 8, 10, 3; cf.: ultor contemptae religionis, Val. Max. 1, 1, 19: Hercules, Hor. Epod. 3, 17: scientia (magica), id. ib. 17, 1: preces, Liv. 9, 20: studium promerendi amoris, Suet. Calig. 3 init.: breve et efficax iter est per exempla, Sen. Ep. 6, 5: admonitiones, id. ib. 8, 2 al.: herba in dolore stomachi, Plin. 27, 13, 109, § 136: preces ad muliebre ingenium, Liv. 1, 9 fin.; so with ad, Sen. Ben. 2, 7 fin.; cf. in the comp., Quint. 6, 1, 41; Plin. Pan. 84: elatine oculorum fluxionibus efficax, Plin. 27, 9, 50, § 74; so with dat., id. 28, 14, 58, § 204; in the sup.: continuatio in peragendis rebus, Liv. 41, 15: frutex efficacissimus contra sagittarum ictus, Plin. 13, 21, 36, § 115; cf.: herba adversus serpentium venena, id. 24, 15, 80, § 130: ad excitandam virtutem, etc., Vell. 1, 8, 1.
Poet., with inf.: (cadus) amara Curarum eluere efficax, Hor. C. 4, 12, 20; Val. Max. 2, 7, 10: cum sit efficacissimum de integro locum exarare, Col. 2, 17, 3: efficacissimum est hic quoque salem superponere, Cels. 4, 4, 16; 4, 22, 11.
Hence, adv.: effĭcācĭter, effectually, powerfully, Quint. 5, 13, 25; Sen. Brev. Vit. 6 et saep.
Comp., Quint. 8, 4, 8; Tac. G. 8; Plin. Ep. 6, 6, 8; Plin. 24, 6, 14, § 23.
Sup., Plin. 26, 12, 79, § 128; 24, 6, 14, § 23; id. Ep. 2, 13 fin.