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.