誠心|せいしんseishin[0]heiban (flat)

1. nounsincerity

• Synonym誠意せいいNeutralThe everyday word for sincerity: acting on conscience, without self-interest. Far more common than 「誠心」, which is formal and mostly appears in 「誠心誠意」.
• Synonym誠実せいじつNeutralDescribes an honest, trustworthy character shown in words and deeds. It judges a person's character, while 「誠心」 refers only to a single sincere feeling.
• Synonym真心まごころNeutralAn unguarded, wholehearted devotion to others. A native word common in speech, it feels warmer and more personal than 「誠心」.
• Synonym至誠しせいWrittenUtmost sincerity, as in the proverb 「至誠天に通ず」. Written style, more solemn than 「誠心」.
• Synonym信しんWrittenKeeping faith, trust, or religious faith. On its own it mostly serves to build compounds; it stresses trustworthiness, not sincerity of heart.
• Synonym真率しんそつWrittenFrank, unaffected honesty. Written style; it stresses being straightforward, whereas 「誠心」 stresses sincerity of feeling.
• Synonym丹心たんしんWrittenLoyal devotion, typically to a lord or one's country. Literary and archaic; unlike 「誠心」, it is not used in everyday dealings with people.
• Synonym至情しじょうWrittenGenuine, deeply felt emotion or natural human warmth. It stresses depth of feeling, while 「誠心」 stresses sincerity of intent.
• Synonym赤心せきしんWrittenPure devotion free of self-interest. Literary and archaic, synonymous with 「丹心」; unlike 「誠心」, it does not suit everyday use.
• Synonym赤誠せきせいWrittenUtterly unfeigned devotion. Written style, stronger and more solemn in tone than 「誠心」.
• Synonym至心ししんWrittenUtmost sincerity, often in Buddhist usage. Written and fairly rare; unlike 「誠心」, it is not a general-purpose word.
• Related誠まことNeutralCovers truth and sincerity alike, and works as the adverb 「誠に」. A broad native word; 「誠心」 means only a sincere heart.
• Related正直しょうじきNeutralHonesty and candor — not lying, speaking plainly. Also adverbial, as in 「正直言って」. It stresses truth-telling rather than sincerity of heart.
• Related本気ほんきCasualBeing in earnest, as opposed to joking. Colloquial and very common; it is about seriousness, not sincerity of feeling.
• Related真面目まじめNeutralSerious, honest, sober conduct. Very common in daily life; it is about a proper attitude, not sincerity of heart specifically.
• Related実じつNeutralRefers to truth or sincerity, and also works as the adverb 「誠に」. A polysemous native word; 「誠心」 is limited to a single sincere feeling.
• Related熱心ねっしんNeutralZealous devotion to a task or cause. It is about drive and enthusiasm, whereas 「誠心」 is about sincerity of heart.
• Related忠誠ちゅうせいNeutralLoyalty to a lord, country, or organization, as in 「忠誠を誓う」. It stresses allegiance to a superior, not sincerity in general.
• Related実直じっちょくNeutralHonest, steady, and dutiful. Describes a person's diligent, dependable character rather than a sincere feeling.
• Related丹精たんせいNeutralLoving care poured into making or raising something, as in 「丹精込めて育てる」. It stresses devoted effort, not sincerity of intent.
• Related実意じついWrittenTrue intentions or genuine, considerate feeling. Written and uncommon; it stresses what one really has in mind, not sincerity as such.
• Antonym虚偽きょぎWrittenAntonym: falsehood and deception. Contrasts with the sincerity of 「誠心」; written and formal.
• Antonym偽心WrittenAntonym: a false, insincere heart. The direct opposite of 「誠心」; rare in actual use.

For a sincere heart, 「誠心」 is written-style and mostly appears in 「誠心誠意」. In everyday speech choose 「誠意」 or 「真心」; for an honest character use 「誠実」; for earnestness use 「本気」 or 「真面目」. The literary compounds 「至誠」, 「赤誠」, 「丹心」, 「赤心」 and the like are solemn or archaic variants; 「正直」 stresses not lying, 「熱心」 enthusiasm, 「忠誠」 allegiance. The antonym is 「虚偽」.

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

1. 真心まごころ。