To Be Effective
To Work Effectively
intransitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means effective. The verb vocab version is to be effective or to work effectively (since "to effective" doesn't make sense).
This word is used to describe something that works effectively and as intended, such as medicine that achieves the desired effect or brakes that effectively stop the car.
What is particularly effective? It's your key (き). It's effective at opening your house door.
肺癌の治療に最も良く効く薬を探しています。
I’m looking for the most effective medicine for treating lung cancer.