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Producing a desired or intended result; having a strong and immediate impact.
The new policy has been effective in reducing costs.
The medicine will be effective in a few hours.
In operation; in effect; currently working or applying.
The law becomes effective next month.
Be careful not to confuse 'effective' with 'efficient'. While both words relate to achieving results, 'effective' focuses on achieving a desired outcome, whereas 'efficient' focuses on achieving that outcome with minimal waste of resources.
From Latin 'effectivus', meaning 'able to produce', from 'effectus', meaning 'a result'.
Often used in formal contexts, such as business, law, and medicine.