Effectual (adjective)

1. Having the power to produce a desired effect or result.
2. Producing a desired effect or result.
3. Capable of producing a desired outcome.

Origin:

From the english word "effect" and the suffix "-ual" which denotes the quality of something.

Examples:

1. The medicine was effectual in treating the patient's symptoms.
2. His efforts were effectual in bringing about change.
3. The negotiations were effectual in resolving the dispute.
4. The lawyer's arguments were effectual in winning the case.
5. The plan was effectual in achieving its goals.