Effectiveness
In Effect, Efficacy
noun
Something's effective power is its effectiveness. If it has effective power, it remains in effect.
This word usually refers to the legal force or effectiveness of a law, agreement, contract, or treaty, but it can also be used to talk about the efficacy of other things, such as medicine.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
その条約は明日で効力を失う。
That treaty will cease to be in effect from tomorrow.
この薬は飲んでから効力を発きするのに数日かかります。
This medicine takes effect several days after you take it.
あなたの今日のプレゼンテーションは、前回に比べて効力が少し弱いような気がしました。
Your presentation today seemed like it was a bit weaker in its effectiveness compared to the last one.