Effete. Barren, unfruitful; decayed, spent, exhausted, worn, wasted, decrepit.
Ant. Vigorous, fertile, prolific, productive, exuberant, luxuriant, rank.
Efficacious. Effectual, effective, active, operative, powerful, adequate, cogent.
Ant. Insufficient, inadequate, ineffectual.
Efficacy. Power, potency, force, competency, strength, effectiveness, vigor, energy, usefulness.
Ant. Inefficacy, incompetency.
Efficiency. Power, strength, capability, virtue, energy, usefulness, productiveness, effectiveness; attentiveness, aptitude, skill, ingenuity, competence, inventiveness, readiness, ingeniousness, faculty, cleverness, genius, acuteness.
Ant. Weakness, inability, incompetence, unproductivity; inattention, awkwardness, absence of mind, thoughtlessness, preoccupation, distraction, laziness, stupidity.
Efficient. Operative, active, potent, efficacious, effective, effectual; able, skilled, ready, energetic, proficient, competent.
Ant. Inactive, impotent, ineffective, abortive; dull, inert, indolent, sluggish, senseless, stupid.