a. [f. L. efficāci- (see prec.) + -OUS: see -ACIOUS.] That produces, or is certain to produce, the intended or appropriate effect; effective. (Said of instruments, methods or actions; not, in prose, of personal agents.)
1528. Roy, Sat. (1845), Goddis worde is so efficacious.
1651. Biggs, New Disp., 35. Lesse efficacious, that is, in plain English ineffectual.
1669. Gale, Crt. Gentiles, I. III. iii. 39. He saies it is the first efficacious cause of the Being of althings.
a. 1679. T. Goodwin, Wks. (1863), VII. 510. God … vouchsafeth … efficacious grace to overcome temptation.
1744. Berkeley, Siris, § 58. 28. Soap therefore is justly esteemed a most efficacious medicine in many distempers.
1830. Lyell, Princ. Geol. (1875), II. III. xli. 421. Variation and Natural Selection will be efficacious in forming distinct races in separate islands.
1860. Mill, Repr. Govt. (1865), 51/2. To provide efficacious securities against this evil.
1873. Browning, Red Cott. Nt.-cap, 497. Be efficacious at the Council there.
