In‐ef′fi‐ca″cious (?), a. [Pref. in- not + efficacious: cf. F. inefficace, L. inefficax.] Not efficacious; not having power to produce the effect desired; inadequate; incompetent; inefficient; impotent. Boyle.
The authority of Parliament must become inefficacious... to restrain the growth of disorders. Burke.
☞ Ineffectual, says Johnson, rather denotes an actual failure, and inefficacious an habitual impotence to any effect. But the distinction is not always observed, nor can it be; for we can not always know whether means are inefficacious till experiment has proved them ineffectual. Inefficacious is therefore sometimes synonymous with ineffectual.