efficacious

An adjective (descriptive word):

Describing thing, or person, producing, or sure to produce, desired effect.

"Efficaciously" (adverb) describing the behaviour of act in such a manner as to effect the desired effect.
I may help to understand that the Latin root for these words is the same as that for "Efficient".

Asprin is truly "efficacious" for the treatment of headaches.

I've never known a teacher to be so consistent in dealing so "efficaciously" with problem students, as he does.

2👍 3👎