誠に・真に・寔に・実に・洵に|まことにmakotoni[0]heiban (flat)

1. adverbreally; truly; very; extremely; exceedingly; sincerely
   遅おくれまして、誠まことに申し訳もうしわけありません。↗

   I'm awfully sorry that I was late.

• Synonym実にじつにNeutralLeans written and is common in exclamations, as in 「実に見事だ」; 「誠に」 is the choice for formal apologies and thanks.
• SynonymまったくNeutralMeans 'entirely' or 'good grief' (「全く知らない」「全くもう」); common in speech and often pairs with negatives.
• SynonymいかにもNeutralStresses that something looks exactly like what it appears to be, as in 「いかにも学者らしい」.
• Synonym甚だはなはだWrittenWritten/formal prose for 'very' (「甚だ遺憾だ」); typically attaches to negative expressions.
• Synonym非常にひじょうにNeutralPlain 'very' (「非常に重要」); somewhat formal but fine in both writing and speech.
• Synonym大変たいへんNeutral'Very' in polite spoken Japanese, as in 「大変お世話になりました」.
• Synonym極めてきわめてWrittenWritten/formal word for 'extremely' (「極めて危険」); signals a very high degree.
• Synonym本当にほんとうにNeutralEveryday 'really' (「本当にありがとう」); 「誠に」 is its formal, ceremonious counterpart.
• Synonym至極しごくNeutral'Extremely', as in 「至極当然」「至極簡単」; can also follow a word, as in 「残念至極」. Written, with an archaic feel.
• Synonym最ももっともNeutralMeans 'most' (「最も高い」); a superlative, not an intensifier of sincerity.
• Synonym至っていたってNeutral'Very', as in 「至って元気」「至って普通」; 「誠に」 by contrast is used mostly in formal thanks and apologies.
• SynonymずいぶんNeutralColloquial 'quite/very' (「随分寒い」); can also imply something is excessive.
• Synonym大いにおおいにNeutral'Greatly/to one's heart's content', as in 「大いに楽しむ」; 「誠に」 focuses on expressing sincerity formally.
• SynonymだいぶNeutralColloquial 'considerably', as in 「だいぶ良くなった」「だいぶ前」; a large degree or amount.
• SynonymたいそうNeutral'Very' with an old-fashioned ring, as in 「大層喜ぶ」; 「誠に」 is for formal addresses.
• SynonymなかなかNeutral'Quite/considerably' (「なかなか上手」); with a negative it means 'not easily'.
• SynonymよほどNeutral'Very/considerably' (「よほど疲れたのだろう」); often carries a nuance of conjecture.
• SynonymひどくNeutral'Terribly/severely' (「ひどく疲れた」); typically with negative expressions.
• SynonymよっぽどCasualColloquial emphatic form of 「余程」 (「よっぽど好きなんだね」), with exaggeration and conjecture.
• SynonymすこぶるWrittenWritten/formal 'very' (「すこぶる元気」) with an old-fashioned flavor.
• Synonym実際にじっさいにNeutralMeans 'actually' (「実際に見た」); stresses that something really happened, not degree.
• Synonym真にしんにWrittenWritten/formal 'truly' (「真に必要なもの」); stresses essence or genuineness.
• Synonym世にもよにもWrittenWritten/formal; 'extremely' with a sense of rarity in this world, as in 「世にも不思議な話」.
• Related誠まことWrittenA noun for sincerity or truth (「誠を尽くす」); as an adverb it sounds archaic.
• RelatedごくNeutral'Quite/very', as in 「ごく普通」「ごく自然」「ごく親しい」; common in speech and writing, while 「誠に」 carries a formal tone.
• Related現にげんにNeutral'Actually/in fact' (「現に見た人がいる」); used to cite real evidence.
• Related本にほんにCasualDialectal, old-fashioned colloquial 'truly' (「ほんにまあ」); rare — say 「本当に」 in daily speech.
• Antonym偽りにNeutralAntonym on the true–false axis; 「偽り」 is really a noun — falseness is usually expressed as 「偽って」 or 「偽りの〜」, not as a standalone adverb.

Use 「誠に」 to say 'truly' with formality and weight, chiefly in polite apologies and thanks like 「誠に申し訳ございません」 and 「誠にありがとうございます」. In everyday speech say 「本当に」; for exclamations 「実に」; for polite spoken emphasis 「大変」; for extreme degree 「極めて」. Words like 甚だ, 頗る, 真に, 世にも and 至極 are written or old-fashioned; 全く, 極, 随分, 大分, 中々 and 余程 are conversational degree words; 実際に and 現に stress that something actually happened rather than degree.

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

1. まことに。本当ほんとうに。