本気|ほんきhonki[0]heiban (flat)

1. no-adjective, na-adjectiveseriousness; earnestness; truth; sanctityusu. 本気で
   ケンさん、君きみは本気ほんきかい。↗

   Are you on the level, Ken?

• Synonym真面目まじめNeutralSerious and earnest as a personality trait; 本気 is about being in earnest on this occasion, not joking.
• Synonym真剣しんけんNeutralSerious and earnest, as in 「真剣勝負」, with a tense, focused attitude; 本気 stresses genuine intent.
• SynonymシリアスNeutralLoanword meaning serious; often describes the grave tone or atmosphere of a work. 本気 is about a person's attitude.
• Synonym真摯しんしWrittenSincere and earnest, a literary word; 本気 is more colloquial.
• Synonym切せつNeutralMeans a limit or end, or 'only'; unrelated in meaning to 本気 and cannot replace it.
• Related一途いちずNeutralSingle-minded devotion, often to love or a career; 本気 focuses on the degree of seriousness.
• Related熱心ねっしんNeutralZealous and enthusiastic; 本気 stresses being serious rather than joking.
• Related一生懸命いっしょうけんめいNeutralDoing something with all one's might; 本気 describes the serious state of mind.
• Related一筋ひとすじNeutralDevoted single-mindedly to one thing; 本気 is about the seriousness of your attitude.
• Related誠まことWrittenGenuine heart and sincerity, with a classical, literary flavor; 本気 is more colloquial.
• Related正直しょうじきNeutralHonesty, not lying; 本気 is about being serious rather than joking.
• Related誠意せいいNeutralGood faith or sincerity; 本気 is about a serious attitude.
• Related誠心せいしんWrittenWritten word for sincerity, rare in use; 本気 is more colloquial.
• Related実じつWrittenThe same word as 「誠」 above, also written 「真」「実」; stresses truth and sincerity, while 本気 is about being in earnest this time, not joking.
• Related誠実せいじつNeutralHonest and trustworthy; 本気 is about the degree of seriousness.
• Related実直じっちょくWrittenHonest, steady and dutiful; 本気 is about being serious rather than joking.
• Related真心まごころNeutralA true, sincere heart; 本気 is about being in earnest.
• Related丹精たんせいNeutralPainstaking, devoted care, as in 「丹精込めて」; 本気 is about the attitude of being serious.
• Related至誠しせいWrittenWritten word for utmost sincerity; 本気 is more colloquial.
• Related真しんWrittenThe same word as 「誠」, also written 「真」; as an adverb it means truly, indeed. 本気 refers to a serious attitude and does not express truth.
• RelatedひたすらWrittenKanji spelling of 「ひたすら」, common from Meiji to prewar; now usually written in kana. Means doing something single-mindedly; 本気 is about being serious, not joking.
• Related懸命けんめいNeutralStraining every effort; 本気 describes the serious state of mind.
• RelatedひたむきNeutralSingle-minded and dedicated, with a positive nuance; 本気 means being in earnest.
• Related生真面目きまじめNeutralOverly serious and rigid, by the book; 本気 is about being in earnest this once.
• Related熱誠ねっせいWrittenWritten word for fervent sincerity; 本気 is more colloquial.
• Antonym冗談じょうだんNeutralA joke or jest; the opposite of 本気, being in earnest.
• Antonym冗談半分じょうだんはんぶんNeutralHalf in jest; the opposite of serious 本気.

Use 「本気」 when someone is in earnest and not joking, as in 「本気で怒る」 or 「本気を出す」. For a serious personality say 「真面目」; for tense, focused seriousness 「真剣」; for single-minded devotion 「一途」; for all-out effort 「一生懸命」. The many sincerity words (誠, 誠意, 真心 and others) stress genuine feeling, and several are literary; 「冗談」 and 「冗談半分」 are the opposites.

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

1. 冗談じょうだんではない真剣しんけんな気持きもち。いい加減かげんでなく本腰ほんごしの入はいった真面目まじめな気持きもち。
2. 冗談じょうだんではなく心こころからそのように思おもっている様子ようす。