Adjective
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having legal efficacy or force
"a sound title to the property"
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producing or capable of producing an intended result or having a striking effect
"an air-cooled motor was more effective than a witch's broomstick for rapid long-distance transportation"-LewisMumford
"effective teaching methods"
"effective steps toward peace"
"made an effective entrance"
"his complaint proved to be effectual in bringing action"
"an efficacious law"