How to say "potency" in Japanese

Choosing the right word

勢力せいりょくJLPT N1approx.Common
nounCovers potency only as power, might, or influence; it is really the word for the strength or influence of a person, group, or organization, and is seldom what you want for 'potency' itself.
地球ちきゅう側がわの圧政あっせいに苦くるしむコロニーの人々ひとびとの中なかで、テロによる現状げんじょう打破だはを目論もくろむ勢力せいりょくが誕生たんじょう。↗
Among the people of the colonies suffering under Earth's tyranny a force emerges intending to overthrow the status quo through terrorism.
効力こうりょくJLPT N2approx.Common
nounCovers potency as effectiveness or efficacy, such as that of a medicine, and also validity, as of a contract or law; this is the word for 'potency' in these senses.
その法律ほうりつはもう効力こうりょくはなくなっている。↗
The law is not in effect any longer.

Use 効力 for potency as effectiveness, efficacy, or validity, as of a drug or a law; choose 勢力 only when potency means the power, might, or influence of a person or group.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

Japanese equivalents

勢力せいりょくinfluence
効力こうりょくeffect
ポテンツpotency
力価りきかtiter

JLPT vocabulary levels are community estimates, not official (no official lists have been published since the 2010 revision).

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