dirty: emphasizes the presence of dirt more than an emotional reaction to it: children ~ from play; or stresses meanness or despicableness: a ~ little secret.     (mean这里是不高尚，是贬义词但贬义不重，可以译成不良)


filthy: carries a strong suggestion of offensiveness and of gradually accumulated dirt that begrimes and besmears: a stained greasy floor, utterly ~; or extreme obscenity: ~ language.      (begrime: 泥污等弄脏) (besmear: 用油粘物弄脏) (stain: 液体等留下的污迹)   (obscene淫秽: 过度涉黄或暴力，如to behave obscenely举止下流)


foul: implies extreme offensiveness and an accumulation of what is rotten and stinking: a ~-smelling open sewer;  or disgusting obscenity or loathsome behavior: a record of ~ deeds.      (sewer下水道)


nasty: applies to what is actually foul or is repugnant to one used to or expecting freshness, cleanliness, or sweetness: it's a ~ job to clean up after a sick cat; although in practice it is often no more than a synonym of unpleasant or disagreeable: his answer gave her a ~ shock.        (repugnant令人厌恶的)


squalid: adds to the idea of dirtiness and filth that of slovenly neglect: living in ~ poverty; or sordid baseness and dirtiness: had a series of ~ affairs.      (sordid肮脏卑鄙: dirty and dishonest脏不诚实: sordid details of their relationship他们关系的肮脏细节) （base卑鄙，比mean不高尚贬义重）


dirty脏的: 仅表示有泥污而不强调情绪反应，或不良让人轻视，filthy肮脏: 强调脏到冒犯(即极其讨厌)，或下流淫秽，foul肮脏: 脏到极端冒犯发腐发臭或淫秽恶心让人厌恶，nasty脏: 事实脏让人厌恶，常仅表示不让人喜欢，squalid肮脏: 增加了邋遢疏于管理的意思，或肮脏卑鄙


记忆方法: 1) 首字母记忆法，DFN想象成DouFuNao豆腐脑，FS想象成FeiShui废水，做豆腐脑剩下的废水<==肮脏  


               2) 肮脏的意思是物质上或道德上不干净纯洁mean either physically or morally unclean or impure.首字母记忆法，DFN想象成DouFuNao豆腐脑，FS想象成FeiShui废水，做豆腐脑剩下的废水<==肮脏      foul和filthy意思相同都表示冒犯和肮脏，但foul更强烈表示"极度"；另外，解释squalid的base表示卑鄙（开头发音都是bei）也比解释dirty的mean（表示不高尚）强烈些