よくよく・良く良く・能く能く・善く善くyokuyoku[0]heiban (flat)

1. adverbcarefully; closely
   間違まちがいをしないようによくよく注意ちゅういしよう。↗

   Let's take the utmost caution against errors.
2. adverbvery; extremely; exceedingly
   そんな話はなしにだまされるなんて、よくよくおめでたいね。↗

   You must be very naive to be taken in by such a story.
3. adverbhave no choice; cannot be helped; unavoidable; inevitable

• RelatedずいぶんNeutralFairly, quite; common in speech and often carrying a sense of surprise, as in 「随分遅いね」. It has no nuance of carefulness.
• Related大変たいへんNeutralVery; common in speech and focused on the size of the degree. It has neither the carefulness nor the last-resort nuance of 「よくよく」.
• RelatedとてもNeutralVery; also used with a negative to mean not at all. The most common colloquial choice, with no nuance of carefulness.
• RelatedひどくNeutralSeverely, terribly; mostly modifies negative things, as in 「ひどく疲れる」.
• Related甚だはなはだWrittenVery; written/formal prose, mostly modifying negative expressions, as in 「甚だ遺憾」.
• RelatedたいそうWrittenVery; slightly old-fashioned. Also a na-adjective, 「大層な」, for things that are grand, impressive or exaggerated.
• Related大いにおおいにNeutralGreatly, to a large degree, as in 「大いに楽しむ」 or 「大いに反省する」; stresses the size of the degree.
• Related至っていたってWrittenExtremely; written/formal prose, as in 「至って元気」 or 「至って普通」.
• Related何ともなんともNeutralReally, indescribably; often exclamatory or followed by a negative, as in 「何とも言えない」.
• RelatedごくNeutralExtremely; common in both speech and writing, as in 「ごく普通」 or 「ごく一部」; stresses the extreme end of the degree.
• Related極めてきわめてWrittenExtremely; formal written prose with an objective tone, and no nuance of carefulness.
• Related非常にひじょうにNeutralVery; the most common formal way to express high degree, but it never carries the last-resort nuance of 「よくよく」.
• Related最ももっともNeutralMainly a superlative, as in 「最も高い」; can also stress an extremely high degree, but lacks the carefulness or last-resort nuances of 「よくよく」.
• RelatedごくごくNeutralExtremely, with a colloquial emphasis; often modifies 「普通」 or 「わずか」. 「よくよく」 instead stresses carefulness or a last resort.
• RelatedすこぶるWrittenExtremely; written prose, slightly old-fashioned and exaggerated in tone, as in 「すこぶる元気」.
• RelatedいたくWrittenDeeply; written/formal prose, typically in 「いたく感動する」.
• Related一方ならずひとかたならずWrittenUnusually, exceptionally; written/formal prose, often used in expressing thanks, as in 「一方ならぬお世話」.
• Related世にもよにもNeutralExtremely, as if rarely seen in this world; as in 「世にも不思議な」.

Use 「よくよく」 for doing something carefully and thoroughly, as in 「よくよく考える」, or for a last resort, as in 「よくよくのことだ」. For plain high degree say 「非常に」 or 「とても」; in written or formal prose 「極めて」 or 「甚だ」; in speech 「随分」.

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

1. 十分じゅうぶんに。念入ねんいりに。
2. 必要ひつよう以上いじょうに。極度きょくどに。