退廃・頽廃|たいはいtaihai[0]heiban (flat)

1. noun, suru verb, intransitive verb(moral) decay; (social) decline; decadence; corruption; degeneration; deterioration
2. noun, suru verb, intransitive verbdecline (in prosperity)

• Synonym衰退すいたいNeutralNeutral and very broad: the general decline of an economy, industry, memory, vigor. Use it for plain decline; 「退廃」 adds the nuance of decadence and corruption.
• Related低下ていかNeutralNeutral. Used for drops in figures, levels or ability (test scores, efficiency); unlike 「退廃」 it has no moral overtones.
• Related減退げんたいNeutralNeutral. Covers the fading of physical functions — energy, appetite, memory; unlike 「退廃」 it concerns bodily or functional decline, not decadence.
• Related減衰げんすいNeutralNeutral but technical, mainly in science and engineering: the attenuation of signals, vibrations, etc.; unrelated to the moral decay of 「退廃」.
• Related悪化あっかNeutralNeutral and very common. Simply 'getting worse' — a condition, situation or relationship deteriorating; no moral-decadence nuance like 「退廃」.
• Related後退こうたいNeutralNeutral. Literally moving backward or retreating; also used for economic recession. Unlike 「退廃」, no sense of moral corruption.
• Related劣化れっかNeutralNeutral. Deterioration in quality or performance — materials, products, images; the go-to word for degradation, not for moral decadence.
• Related下り坂くだりざかCasualColloquial and vivid: literally a downhill slope, figuratively being on the decline — health, popularity, a career. Lighter than 「退廃」.
• Related衰弱すいじゃくNeutralNeutral. Physical weakness or debility — the body, nerves, eyesight losing strength; unlike 「退廃」 it is about vigor, not decadence.
• Related退潮たいちょうWrittenWritten/formal. An ebbing tide, figuratively the receding of influence or a trend; unlike 「退廃」 it suggests waning force, not decadence.
• Related没落ぼつらくNeutralNeutral. The downfall or ruin of a family, class or institution — falling from former standing; 「退廃」 instead evokes decadent atmosphere.
• Related衰えおとろえNeutralNative Japanese word (noun from 衰える) for the waning of strength, vigor or influence with age; unlike 「退廃」 it has no moral coloring.
• Related退勢たいせいWrittenWritten/formal. Refers to waning power or momentum — the decline of a position or situation; 「退廃」 instead targets moral decadence and social decay.
• Related衰勢すいせいWrittenWritten/formal and rare. Describes a declining trend or momentum; unlike 「退廃」 it carries no sense of moral decadence.
• Related萎靡いびWrittenWritten/formal and rare. Means listlessness, losing vigor and drive; unlike 「退廃」 it describes a person's enervation rather than social decadence.
• Related衰微すいびWrittenWritten/formal. The fading of something once flourishing — a family, a tradition; unlike 「退廃」 it lacks the nuance of moral decadence.
• Related凋残ちょうざんWrittenWritten/formal, archaic and literary: flowers and plants withering, hence elegant decay; far more poetic than 「退廃」.
• Related凋落ちょうらくWrittenWritten/formal. Withering and falling of flowers, or the decline of a family's fortunes, with a melancholy tone; 「退廃」 stresses decadence instead.
• Related衰滅すいめつWrittenWritten/formal. The decline and eventual disappearance of something once prosperous; stronger than 「退廃」, ending in ruin or extinction.
• Related式微しきびWrittenWritten/formal, archaic and literary: an extreme, deep-seated decline; far more bookish than 「退廃」 and without its decadent nuance.
• Related落潮らくちょうWrittenWritten/formal. A falling tide, figuratively one's fortunes on the ebb; unlike 「退廃」 it pictures decline, not moral decay.
• Antonym繁栄はんえいNeutralAntonym. Prosperity and flourishing — the opposite of the decadent, decaying state 「退廃」 describes.
• Antonym隆盛りゅうせいWrittenAntonym, written/formal. Vigorous flourishing or prosperity; stands at the opposite pole from the social decay of 「退廃」.

Use 「退廃」 for moral decadence, corrupt atmosphere or social decay, as in 「退廃的な雰囲気」 or 「道徳の退廃」. For plain decline say 「衰退」 or 「没落」, for deterioration 「悪化」, for falling quality or performance 「劣化」. Antonyms are 「繁栄」 and 「隆盛」.

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

1. 崩くずれ廃すたれること。
2. 不健全ふけんぜんになること。