efficacious
UK/.efi'keiʃәs/US
GREC1
Definitions
adj.
(Formal) producing the intended result; effective, especially of a remedy or treatment
（正式）有效的，灵验的（尤指药物、疗法）
Root Breakdown
Root-derivedef- (ex-, out) + fic (the weakened fac, 'do/work') + -acious (tending to) = 'tending to work out the result.' Same core as effect and efficient — something that gets the result done.
Root fac still carries 273 more wordsWhy It Means This
A formal, almost clinical word. You meet it in medical and scientific writing — 'an efficacious vaccine' — where 'effective' would do in everyday speech. The fic root is doing exactly what it does in efficient: producing a result.
Example Sentences
- 1.
Clinical trials showed the drug to be highly efficacious.
- 2.
The new policy proved efficacious in reducing waste.