deterioration: implies impairment of such valuable qualities as vigor, resilience, or usefulness: the ~ of her memory in recent years.   deteriorate和impair互释，都表示损害降低，使不再complete and efficient健全有效，用于健康记忆力量等，如本例近年记忆下降，如years of smoking impaired his health损害健康         vitality活力强调生存力繁殖力，vigor也叫活力，但强调力量体力耐力


degeneration: stresses physical, intellectual, or moral retrogression: the ~ of his youthful idealism.   （来自词根GEN表示出生birth，如gene基因genesis创世纪generation一代人genre类型体裁carcinogen致癌物，词根DE表示down往下，这个词比下边的颓废堕落decadence严重地多，如inactivity can make your bones to degenerate长期不活动会导致骨骼退化，如a degenerative disease退化性疾病，如social/moral degeneration社会堕落倒退/道德沦丧，如degenerate criminals堕落的罪犯）  physical 1、物理的，指可以"测量"的 2、身体的, 是bodily肉体的委婉说法     retrograde向后后退to move backwards，如a retrograde flow/step/development/motion回流/后退/退化/天体逆行


decadence: presupposes a previous attainment of maturity or excellence and implies a turn downward with a consequent loss of vitality or energy: cited rock music as a sign of cultural ~.    （颓废表示"意志消沉精神萎靡"，decadence还表示历史上的颓废主义或颓废派，最先在1880年用来称呼一群放浪的法国青年诗人，他们反对受道德或生活目标的约束，主张"为艺术而艺术"。decadence还表示放纵贪图享受implies luxurious self-indulgence，如cream cakes on a Wednesday—pure decadence星期三吃奶油蛋糕——完全是放纵堕落）  又如he denounced Western decadence他抨击了西方的颓废


decline: suggests a more marked downward direction and greater momentum as well as more obvious evidence of deterioration: the meteoric rise and ~ of his career.    如my grandmother's health/condition has been declining rapidly祖母健康迅速恶化  "但也可以表示逐渐下降"，如a rapid/sharp/gradual decline迅速/急剧/逐渐下降    momentum动量冲力势头  流星的,迅速成功的


deterioration下降损坏: 表示体力柔韧度功能等受损，degeneration堕落倒退: 指身体精神道德等严重倒退，decadence颓废堕落: 表示之前成熟优秀，后变得萎靡，decline下降: 可以表示更明显、速度更快的下降，或泛指下降


记忆方法: 1）首字母DDDD想成4个Down<==下降          "降"的古字形像"两脚交替沿山而下"，本义是"从高处走下来"，与"陟（向上行走）"字义正好相反。由本义引申，泛指"下降落下"，如出世出生叫降生降临，"以降"表示一段时间或一片范围。都反映出从高处向低处的变动。降还指"向对方屈服，或制服、使驯服"，如投降降军降服受降    "退"的意思是"向后移动"，与"进"相对，从彳从日从攵。"彳"表示"步行"，"攵"表示"足的反写"。本义是"向后走"，如退步退路退却退让倒退，引申为"离开"，如退席退伍退职退休引退退毛退色

         2）下降的意思是品质活力等由高到低mean a falling from a higher to a lower level in quality, character, or vitality.    level水平，sea level海平面