Effective (adjective)

1. Capable of producing a desired effect or result; efficient.
2. Having legal force or effect; valid.
3. Producing a significant impact; influential.
4. Producing results; producing the intended or expected outcome.

Origin:

From middle english effectif, from old french effectif, from latin effectīvus, from effectus ("a working, operation"), from efficere ("to do, make, perform").

Examples:

1. The new policy was effective in reducing crime.
2. Her argument was effective in convincing the audience.
3. The medicine was effective in treating his illness.
4. The advertisement was effective in increasing sales.
5. The solution was effective in solving the problem.