How to say "infidelity" in Japanese

• 背信はいしんCommon
  suru verb, no-adjectiveCovers the betrayal sense of 'infidelity' rather than romantic cheating; it suggests treachery or a breach of trust. Typical contexts are disloyalty to a country, organization, or ally more than a spouse.
  この報告ほうこくは彼かれの背信はいしんを裏付うらづけしている。↗

  This report confirms his betrayal.
• 浮気うわきJLPT N1approx.Common
  noun, na-adjective, suru verb, intransitive verbThe everyday word for infidelity as cheating on a partner, carrying a nuance of flightiness or wantonness. It is what you would naturally use for a boyfriend, girlfriend, or spouse straying, whether briefly or habitually.
  彼女かのじょは浮気うわきな女おんなで本当ほんとうに誰だれでも相手あいてにする。↗

  She is a loose woman and will honestly go with anyone.
• 不義ふぎCommon
  no-adjectivePoints to the adultery sense of 'infidelity', a serious violation of marital faithfulness, with the glosses also noting cuckoldry. Use it when the emphasis is on the gravity of adultery rather than lighthearted cheating.

Use 浮気 for casual or romantic cheating in a relationship, 不義 for adultery in marriage, and 背信 mainly for betrayal in a broader, often non-romantic sense.

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

• 背信はいしんbetrayal
• 不貞ふていunfaithfulness
• 不忠ふちゅうdisloyalty
• 不信心ふしんじんimpiety
• 不義密通ふぎみっつうadultery
• 不信仰ふしんこうlack of faith
• 浮気うわきinfidelity
• 不義ふぎadultery