effectual

effective, effectual, efficient, efficacious mean producing or capable of producing a result. effective stresses the actual production of or the power to produce an effect.

• • an effective rebuttal

effectual suggests the accomplishment of a desired result especially as viewed after the fact.

• • the measures to stop the pilfering proved effectual

efficient suggests an acting or a potential for action or use in such a way as to avoid loss or waste of energy in effecting, producing, or functioning.

• • an efficient small car

efficacious suggests possession of a special quality or virtue that gives effective power.

• • a detergent that is efficacious in removing grease