Effectual means producing or capable of producing a desired effect.
Effectual is an adjective.
Synonyms: capable, adequate, competent.
Antonyms: ineffectual, inadequate, incapable.
Note: Effectual, effective, efficacious, and efficient share a central meaning of producing or being capable of producing a desired effect. Effectual implies adequately, but not necessarily masterfully, answering a basic purpose.
The seminar wasn't exceptional, but it was effectual; we came away with a basic understanding of the concept.
Even after years of marriage, Swapna has not yet come up with an effectual method of sleeping next to her snoring husband.
My method of solving the problem may not be the most efficient one but it is still effectual.