How to say "decay" in Japanese

• くさるJLPT N3approx.Common
  godan verb, intransitive verbCovers the everyday sense of organic matter rotting, going bad or spoiling. Use it for food, fruit, meat, teeth or wood decaying; it is the basic verb for physical decay.
  これらのオレンジは腐くさっている。↗

  These oranges have gone bad.
• 衰退すいたいCommon
  noun, suru verb, intransitive verbAn abstract, figurative decay meaning decline or waning. Choose it when an economy, industry, memory, tradition or someone's powers are deteriorating rather than when anything is literally rotting.
  ４７５年ねんはローマ帝国ていこくの「衰退すいたい」を示しめす年としではあっても、「滅亡めつぼう」を意味いみする年としではありません。↗

  Although 475AD is the year that shows the 'decline' of the Roman Empire, it is not the year of its 'fall'.
• 減衰げんすいCommon
  noun, suru verb, intransitive verbA technical decay meaning gradual attenuation or damping of something measurable, such as a signal, sound, radiation or energy fading over distance or time. Use it mainly in scientific and engineering contexts.
• 腐食ふしょくCommon
  noun, suru verb, transitive verb, intransitive verbDecay by corrosion or erosion, typically of metal, caused by chemical action such as rusting. Use it for corroded pipes, machinery or structures; it is not the word for rotting food.
  その神社じんじゃの腐食ふしょくの原因げんいんの一ひとつは酸性雨さんせいうである。↗

  The decay of the shrine is due, in part, to acid rain.
• 腐りくさりCommon
  nounEssentially the noun form related to くさる, denoting rottenness or the decay of organic matter. It also extends to moral corruption; use it when naming the state of being rotten rather than the process.

For physical rotting of organic matter use 「くさる」, for abstract decline of strength, economies or systems use 衰退, for technical gradual loss of signal, energy or value use 減衰, for corrosion of metal or erosion use 腐食, and 「腐り」 is the noun form of decayed, rotten matter.

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

• くさるto rot
• 衰退すいたいdecline
• 減衰げんすいattenuation
• 腐食ふしょくrot
• 腐りくさりrottenness
• 衰えるおとろえるto become weak
• 荒廃こうはいruin
• 減退げんたいdecline
• 朽ちるくちるto rot
• ディケイdecay
• 腐朽ふきゅうdecay
• 朽廃きゅうはいdecay
• 廃滅はいめつdecay
• 立ち下がりたちさがりdecay (e.g. charge, signal)
• 凋落ちょうらくdecline
• 衰微すいびdecline
• 退勢たいせいdecline
• 萎靡いびdecline
• 衰勢すいせいdownward tendency
• 式微しきびextreme decline
• 崩解ほうかいdisintegration
• 曝れるされるto weather (e.g. by long exposure to sun or rain)
• 退廃たいはい(moral) decay
• 廃退はいたい(moral) decay
• 壊変かいへん(radioactive) decay
• 腐敗ふはいcorruption
• 崩壊ほうかい(radioactive) decay